Filed Pursuant to Rule 497
Registration No. 333-214767

PROSPECTUS SUPPLEMENT

(To prospectus dated September 7, 2017)

$75,000,000

5.25% Notes due 2025

We are an internally-managed, non-diversified, closed-end investment company that has elected to be regulated as a business development company under the Investment Company Act of 1940, as amended, or the 1940 Act. Our investment objective is to maximize our portfolio’s total return by generating current income from our debt investments and capital appreciation from our warrant and equity-related investments.

We are offering $75,000,000 in aggregate principal amount of 5.25% notes due 2025, or the “Notes.” The Notes will mature on April 30, 2025. We will pay interest quarterly on the Notes on January 30, April 30, July 30 and October 30 of each year, beginning on July 30, 2018. We may redeem the Notes in whole or in part at any time or from time to time, at the redemption price set forth under “Specific Terms of the Notes and the Offering—Optional Redemption” in this prospectus supplement. The Notes will be issued in minimum denominations of $25 and integral multiples of $25 in excess thereof.

The Notes will be our direct unsecured obligations and rank pari passu, or equally in right of payment, with all outstanding and future unsecured unsubordinated indebtedness issued by Hercules Capital, Inc.

We intend to apply to list the Notes on the New York Stock Exchange, or NYSE, and we expect trading in the Notes on the NYSE to begin within 30 days of the original issue date under the symbol “HCXZ.” The Notes are expected to trade “flat,” which means that purchasers will not pay, and sellers will not receive, any accrued and unpaid interest on the Notes that is not reflected in the trading price. Currently, there is no public market for the Notes.

An investment in the Notes involves risks that are described in the “Supplementary Risk Factors” section beginning on page S-14 in this prospectus supplement and the “Risk Factors” section beginning on page 14 of the accompanying prospectus.

This prospectus supplement and the accompanying prospectus contain important information you should know before investing in the Notes. Please read this prospectus supplement and the accompanying prospectus before investing and keep it for future reference. We file annual, quarterly and current reports, proxy statements and other information about us with the Securities and Exchange Commission. This information is available free of charge by contacting us at 400 Hamilton Avenue, Suite 310, Palo Alto, California 94301, or by telephone by calling collect at (650) 289-3060 or on our website at www.htgc.com. The information on the websites referred to herein is not incorporated by reference into this prospectus supplement or the accompanying prospectus. The SEC also maintains a website at www.sec.gov that contains information about us.

The underwriters may also purchase up to an additional $11,250,000 total aggregate principal amount of Notes offered hereby, to cover overallotments, if any, within 30 days of the date of this prospectus supplement. If the underwriters exercise this option in full, the total public offering price will be $86,250,000, the total sales load (underwriting discounts and commissions) paid by us will be $2,357,500, and total proceeds, before expenses, will be $83,892,500.

THE NOTES ARE NOT DEPOSITS OR OTHER OBLIGATIONS OF A BANK AND ARE NOT INSURED BY THE FEDERAL DEPOSIT INSURANCE CORPORATION OR ANY OTHER GOVERNMENT AGENCY.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus supplement or the accompanying prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

Delivery of the Notes in book-entry form only through The Depository Trust Company will be made on or about April 26, 2018.

Joint Book-Running Managers

Lead Manager

Janney Montgomery Scott

Co-Managers

The date of this prospectus supplement is April 23, 2018.

You should rely only on the information contained in this prospectus supplement and the accompanying prospectus. We have not, and the underwriters have not, authorized any other person to provide you with different information. If anyone provides you with different or inconsistent information, you should not rely on it. We are not, and the underwriters are not, making an offer to sell these securities in any jurisdiction where the offer or sale is not permitted. You should assume that the information contained in this prospectus supplement and the accompanying prospectus is accurate only as of the date on the front cover of this prospectus supplement or such prospectus, as applicable. Our business, financial condition, results of operations and prospects may have changed since that date.

This document is in two parts. The first part is this prospectus supplement, which describes the terms of this offering and also adds to and updates information contained in the accompanying prospectus. The second part is the accompanying prospectus, which gives more general information and disclosure. To the extent the information contained in this prospectus supplement differs from the information contained in the accompanying prospectus, the information in this prospectus supplement shall control. You should read this prospectus supplement and the accompanying prospectus together with the additional information described under the heading, “Available Information” before investing in our Notes.

TABLE OF CONTENTS

Prospectus Supplement

Prospectus

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FORWARD-LOOKING STATEMENTS

The matters discussed in this prospectus supplement and the accompanying prospectus, as well as in future oral and written statements by management of Hercules Capital, Inc. that are forward-looking statements are based on current management expectations that involve substantial risks and uncertainties which could cause actual results to differ materially from the results expressed in, or implied by, these forward-looking statements. Forward-looking statements relate to future events or our future financial performance. We generally identify forward-looking statements by terminology such as “may,” “will,” “should,” “expects,” “plans,” “anticipates,” “could,” “intends,” “target,” “projects,” “contemplates,” “believes,” “estimates,” “predicts,” “potential” or “continue” or the negative of these terms or other similar expressions. Important assumptions include our ability to originate new investments, achieve certain margins and levels of profitability, the availability of additional capital, and the ability to maintain certain debt to asset ratios. In light of these and other uncertainties, the inclusion of a projection or forward-looking statement in this prospectus should not be regarded as a representation by us that our plans or objectives will be achieved. The forward-looking statements contained in this prospectus supplement and the accompanying prospectus include statements as to:

For a discussion of factors that could cause our actual results to differ from forward-looking statements contained in this prospectus supplement and the accompanying prospectus, please see the discussion under “Supplementary Risk Factors” in this prospectus supplement and “Risk Factors” in the accompanying prospectus.

You should not place undue reliance on these forward-looking statements. The forward-looking statements made in this prospectus relate only to events as of the date on which the statements are made and are excluded from the safe harbor protection provided by Section 27A of the Securities Act of 1933, or the Securities Act. We undertake no obligation to update any forward-looking statement to reflect events or circumstances occurring after the date of this prospectus supplement.

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INDUSTRY AND MARKET DATA

We have compiled certain industry estimates presented in this prospectus supplement and the accompanying prospectus from internally generated information and data. While we believe our estimates are reliable, they have not been verified by any independent sources. The estimates are based on a number of assumptions, including increasing investment in venture capital and private equity-backed companies. Actual results may differ from projections and estimates, and this market may not grow at the rates projected, or at all. If this market fails to grow at projected rates, our business and the market price of our securities, including the Notes, could be materially adversely affected.

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SUPPLEMENTARY RISK FACTORS

Investing in our securities involves a number of significant risks. Before you invest in our securities, you should be aware of various risks, including those described below and those set forth in the accompanying prospectus. You should carefully consider these risk factors, together with all of the other information included in this prospectus supplement and the accompanying prospectus, before you decide whether to make an investment in our securities. The risks set out below and in the accompanying prospectus are not the only risks we face. Additional risks and uncertainties not presently known to us or not presently deemed material by us may also impair our operations and performance. If any of the following events occur, our business, financial condition, results of operations and cash flows could be materially and adversely affected which could materially adversely affect our ability to repay principal and interest on the Notes. In addition, the market price of the Notes and our net asset value could decline, and you may lose all or part of your investment. The risk factors described below, together with those set forth in the accompanying prospectus, are the principal risk factors associated with an investment in our securities, including the Notes, as well as those factors generally associated with an investment company with investment objectives, investment policies, capital structure or trading markets similar to ours.

Risks Related to the Notes

The Notes will be unsecured and therefore will be effectively subordinated to any secured indebtedness we have currently incurred or may incur in the future.

The Notes will not be secured by any of our assets or any of the assets of our subsidiaries. As a result, the Notes are effectively subordinated to any secured indebtedness we or our subsidiaries have currently incurred and may incur in the future (or any indebtedness that is initially unsecured to which we subsequently grant security) to the extent of the value of the assets securing such indebtedness. In any liquidation, dissolution, bankruptcy or other similar proceeding, the holders of any of our existing or future secured indebtedness and the secured indebtedness of our subsidiaries may assert rights against the assets pledged to secure that indebtedness in order to receive full payment of their indebtedness before the assets may be used to pay other creditors, including the holders of the Notes. As of December 31, 2017, we had no outstanding borrowings under our Union Bank Facility, which is secured by debt investments in our portfolio companies and related assets, and no outstanding borrowings under our Wells Facility, which is secured by loans in the borrowing base for the Wells Facility.

The Notes will be structurally subordinated to the indebtedness and other liabilities of our subsidiaries.

The Notes are obligations exclusively of Hercules Capital, Inc. and not of any of our subsidiaries. None of our subsidiaries is a guarantor of the Notes and the Notes are not required to be guaranteed by any subsidiaries we may acquire or create in the future. A significant portion of the indebtedness required to be consolidated on our balance sheet is held through our SBIC subsidiaries. For example, at December 31, 2017, we have issued $190.2 million in SBA-guaranteed debentures in our SBIC subsidiaries. The assets of such subsidiaries are not directly available to satisfy the claims of our creditors, including holders of the Notes. See “Management’s Discussion and Analysis of Financial Condition and Results of Operations—Financial Condition, Liquidity and Capital Resources” in this prospectus supplement for more detail on the SBA-guaranteed debentures.

Except to the extent we are a creditor with recognized claims against our subsidiaries, all claims of creditors (including trade creditors), if any, of our subsidiaries will have priority over our equity interests in such subsidiaries (and therefore the claims of our creditors, including holders of the Notes) with respect to the assets of such subsidiaries. Even if we are recognized as a creditor of one or more of our subsidiaries, our claims would still be effectively subordinated to any security interests in the assets of any such subsidiary and to any indebtedness or other liabilities of any such subsidiary senior to our claims. Consequently, the Notes will be structurally subordinated to all indebtedness and other liabilities (including trade payables) of any of our subsidiaries and any subsidiaries that we may in the future acquire or establish as financing vehicles or otherwise.

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As of December 31, 2017, we had no outstanding borrowings under our Wells Facility, no outstanding borrowings under our Union Bank Facility, and approximately $190.2 million of indebtedness outstanding incurred by our SBIC subsidiaries, HT II and HT III. All of such indebtedness would be structurally senior to the Notes. In addition, our subsidiaries may incur substantial additional indebtedness in the future, all of which would be structurally senior to the Notes.

The indenture under which the Notes will be issued contains limited protection for holders of the Notes.

The indenture under which the Notes will be issued offers limited protection to holders of the Notes. The terms of the indenture and the Notes do not restrict our or any of our subsidiaries’ ability to engage in, or otherwise be a party to, a variety of corporate transactions, circumstances or events that could have an adverse impact on your investment in the Notes. In particular, the terms of the indenture and the Notes will not place any restrictions on our or our subsidiaries’ ability to:

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In addition, the indenture will not require us to purchase the Notes in connection with a change of control or any other event.

Furthermore, the terms of the indenture and the Notes do not protect holders of the Notes in the event that we experience changes (including significant adverse changes) in our financial condition, results of operations or credit ratings, as they do not require that we or our subsidiaries adhere to any financial tests or ratios or specified levels of net worth, revenues, income, cash flow, or liquidity.

Our ability to recapitalize, incur additional debt and take a number of other actions that are not limited by the terms of the Notes may have important consequences for you as a holder of the Notes, including making it more difficult for us to satisfy our obligations with respect to the Notes or negatively affecting the trading value of the Notes.

Certain of our current debt instruments include more protections for their holders than the indenture and the Notes. See “Risk Factors—In addition to regulatory requirements that restrict our ability to raise capital, our 2022 Notes, 2024 Notes, 2022 Convertible Notes, and Credit Facilities contain various covenants which, if not complied with, could require accelerated repayment under the facility or require us to repurchase the 2022 Notes, 2024 Notes, 2022 Convertible Notes thereby materially and adversely affecting our liquidity, financial condition, results of operations and ability to pay distributions” in the accompanying prospectus. In addition, other debt we issue or incur in the future could contain more protections for its holders than the indenture and the Notes, including additional covenants and events of default. The issuance or incurrence of any such debt with incremental protections could affect the market for, and trading levels and prices of, the Notes.

Our amount of debt outstanding may increase as a result of this offering. Our current indebtedness could adversely affect our business, financial condition and results of operations and our ability to meet our payment obligations under the Notes and our other debt.

The use of debt could have significant consequences on our future operations, including:

Any of the above-listed factors could have an adverse effect on our business, financial condition and results of operations and our ability to meet our payment obligations under the Notes and our other debt.

Our ability to meet our payment and other obligations under our financing arrangements depends on our ability to generate significant cash flow in the future. This, to some extent, is subject to general economic, financial, competitive, legislative and regulatory factors as well as other factors that are beyond our control. We cannot assure you that our business will generate cash flow from operations, or that future borrowings will be available to us under our financing arrangements or otherwise, in an amount sufficient to enable us to meet our payment obligations under the Notes and our other debt and to fund other liquidity needs. If we are not able to generate sufficient cash flow to service our debt obligations, we may need to refinance or restructure our debt,

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including the Notes, sell assets, reduce or delay capital investments, or seek to raise additional capital. If we are unable to implement one or more of these alternatives, we may not be able to meet our payment obligations under the Notes and our other debt.

The optional redemption provision may materially adversely affect your return on the Notes.

The Notes will be redeemable in whole or in part upon certain conditions at any time, or from time to time, at our option on or after April 30, 2021. We may choose to redeem the Notes at times when prevailing interest rates are lower than the interest rate paid on the Notes. In this circumstance, you may not be able to reinvest the redemption proceeds in a comparable security at an effective interest rate as high as the Notes being redeemed.

An active trading market for the Notes may not develop or be maintained, which could limit the market price of the Notes or your ability to sell them.

The Notes are a new issue of debt securities for which there currently is no trading market. We intend to apply to list the Notes on the NYSE within 30 days of the original issue date. Although we expect the Notes to be listed on the NYSE, we cannot provide any assurances that an active trading market will develop for the Notes or that you will be able to sell your Notes. If the Notes are traded after their initial issuance, they may trade at a discount from their initial offering price depending on prevailing interest rates, the market for similar securities, our credit ratings, general economic conditions, our financial condition, performance and prospects and other factors. The underwriters have advised us that they intend to make a market in the Notes, but they are not obligated to do so. The underwriters may discontinue any market-making in the Notes at any time at their sole discretion. Accordingly, we cannot assure you that an active trading market will develop for the Notes, that you will be able to sell your Notes at a particular time or that the price you receive when you sell will be favorable. To the extent an active trading market does not develop, the liquidity and trading price for the Notes may be harmed. Accordingly, you may be required to bear the financial risk of an investment in the Notes for an indefinite period of time.

A downgrade, suspension or withdrawal of a credit rating assigned by a rating agency to us or our unsecured debt, if any, or change in the debt markets could cause the liquidity or market value of the Notes to decline significantly.

Our credit ratings are an assessment by rating agencies of our ability to pay our debts when due. Consequently, real or anticipated changes in our credit ratings will generally affect the market value of the Notes. These credit ratings may not reflect the potential impact of risks relating to the structure or marketing of the Notes. Credit ratings are not a recommendation to buy, sell or hold any security, and may be revised or withdrawn at any time by the issuing organization in its sole discretion. Neither we nor any underwriter undertakes any obligation to maintain our credit ratings or to advise holders of Notes of any changes in our credit ratings. There can be no assurance that our credit ratings will remain for any given period of time or that such credit ratings will not be lowered or withdrawn entirely by the rating agencies if in their judgment future circumstances relating to the basis of the credit ratings, such as adverse changes in our company, so warrant. The conditions of the financial markets and prevailing interest rates have fluctuated in the past and are likely to fluctuate in the future, which could have an adverse effect on the market prices of the Notes.

If we Default on our obligations to pay our other indebtedness, we may not be able to make payments on the Notes.

Any default under the agreements governing our indebtedness, including a default under the Wells Facility, the Union Bank Facility, the 2022 Notes, the 2024 Notes, the 2022 Convertible Notes, and the 2021 Asset-Backed Notes or other indebtedness to which we may be a party, that is not waived by the required lenders or holders, and the remedies sought by the holders of such indebtedness, could make us unable to pay principal, premium, if any, and interest on the Notes and substantially decrease the market value of the Notes. If we are unable to generate sufficient cash flow and are otherwise unable to obtain funds necessary to meet required

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payments of principal, premium, if any, and interest on our indebtedness, or if we otherwise fail to comply with the various covenants, including financial and operating covenants, in the instruments governing our indebtedness, we could be in default under the terms of the agreements governing such indebtedness. In the event of such default, the holders of such indebtedness could elect to declare all the funds borrowed thereunder to be due and payable, together with accrued and unpaid interest, the lenders under the Wells Facility and the Union Bank Facility or other debt we may incur in the future could elect to terminate their commitments, cease making further loans and institute foreclosure proceedings against our assets, and we could be forced into bankruptcy or liquidation. If our operating performance declines, we may in the future need to seek to obtain waivers from the required lenders under the Wells Facility or Union Bank Facility or the required holders of our 2022 Notes, our 2024 Notes, 2022 Convertible Notes, 2021 Asset-Backed Notes or other debt that we may incur in the future to avoid being in default. If we breach our covenants under the Wells Facility, Union Bank Facility, the 2022 Notes, the 2024 Notes, the 2022 Convertible Notes, the 2021 Asset-Backed Notes or other debt and seek a waiver, we may not be able to obtain a waiver from the required lenders or holders. If this occurs, we would be in default under the Wells Facility or Union Bank Facility, the 2022 Notes, the 2024 Notes, the 2022 Convertible Notes, the 2021 Asset-Backed Notes or other debt, as applicable, the lenders or holders could exercise their rights as described above, and we could be forced into bankruptcy or liquidation. If we are unable to repay debt, lenders having secured obligations, including the lenders under the Wells Facility and the Union Bank Facility, could proceed against the collateral securing the debt. Because the Wells Facility and the Union Bank Facility have, and any future credit facilities will likely have, customary cross-default provisions, if the indebtedness under the Notes, the Wells Facility, Union Bank Facility, the 2022 Notes, the 2024 Notes, the 2022 Convertible Notes or the 2021 Asset-Backed Notes or under any future credit facility is accelerated, we may be unable to repay or finance the amounts due. See “Specific Terms of the Notes and the Offering” in this prospectus supplement.

FATCA withholding may apply to payments to certain foreign entities.

Payments made under the Notes to a foreign financial institution or non-financial foreign entity (including such an institution or entity acting as an intermediary) may be subject to a U.S. withholding tax of 30% under U.S. Foreign Account Tax Compliance Act provisions of the Code (commonly referred to as “FATCA”). This U.S. withholding tax generally applies to payments of interest on the Notes as well as, after December 31, 2018, to any payments of gross proceeds (including principal payments) from the sale, redemption, retirement or other disposition of the Notes, unless the foreign financial institution or non-financial foreign entity complies with certain information reporting, withholding, identification, certification and related requirements imposed by FATCA. Depending upon the status of a holder and the status of an intermediary through which any Notes are held, the holder could be subject to this 30% U.S. withholding tax in respect of any interest paid on the Notes as well as any proceeds from the sale, redemption, retirement or other disposition of the Notes. Persons located in jurisdictions that have entered into an intergovernmental agreement with the United States to implement FATCA may be subject to different rules. You should consult your own tax advisors regarding FATCA and how it may affect your investment in the Notes. See “Certain United States Federal Income Tax Considerations—Taxation of Note Holders—FATCA” in this prospectus supplement for further information.

Risks Related to our Business Structure

As an internally managed business development company, we are subject to certain restrictions that may adversely affect our business.

As an internally managed business development company, the size and categories of our assets under management is limited, and we are unable to offer as wide a variety of financial products to prospective portfolio companies and sponsors (potentially limiting the size and diversification of our asset base). We therefore may not achieve efficiencies of scale and greater management resources available to externally managed business development companies.

Additionally, as an internally managed business development company, our ability to offer more competitive and flexible compensation structures, such as offering both a profit sharing plan and an equity incentive plan, is subject to the limitations imposed by the 1940 Act, which limits our ability to attract and retain

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talented investment management professionals. As such, these limitations could inhibit our ability to grow, pursue our business plan and attract and retain professional talent, any or all of which may have a negative impact on our business, financial condition and results of operations.

As an internally managed business development company, we are dependent upon key management personnel for their time availability and for our future success, particularly Manuel A. Henriquez, and if we are not able to hire and retain qualified personnel, or if we lose any member of our senior management team, our ability to implement our business strategy could be significantly harmed.

As an internally managed business development company, our ability to achieve our investment objectives and to make distributions to our stockholders depends upon the performance of our senior management. We depend upon the members of our senior management, particularly Mr. Henriquez, as well as other key personnel for the identification, final selection, structuring, closing and monitoring of our investments. These employees have critical industry experience and relationships on which we rely to implement our business plan. If we lose the services of Mr. Henriquez or any senior management members, we may not be able to operate the business as we expect, and our ability to compete could be harmed, which could cause our operating results to suffer. Furthermore, we do not have an employment agreement with Mr. Henriquez or our senior management that restricts them from creating new investment vehicles subject to compliance with applicable law. We believe our future success will depend, in part, on our ability to identify, attract and retain sufficient numbers of highly skilled employees. If we do not succeed in identifying, attracting and retaining such personnel, we may not be able to operate our business as we expect. In connection with our recruiting, branding and marketing efforts, we may, among other things, make charitable contributions in amounts we believe to be immaterial. We believe that many of these contributions help us raise our profile in the communities and benefit us in attracting and retaining talent and investment opportunities.

As an internally managed business development company, our compensation structure is determined and set by our Board of Directors. This structure currently includes salary and bonus and incentive compensation, which is issued through grants and subsequent vesting of restricted stock. We are not generally permitted by the 1940 Act to employ an incentive compensation structure that directly ties performance of our investment portfolio and results of operations to compensation owing to our granting of restricted stock as incentive compensation.

Members of our senior management may receive offers of more flexible and attractive compensation arrangements from other companies, particularly from investment advisers to externally managed business development companies that are not subject to the same limitations on incentive-based compensation that we, as an internally managed business development company are subject to. We do not currently have agreements with certain members of our senior management that prohibit them from leaving and competing with our business and certain States limit our ability to have such agreements. In addition, the evaluation of alternative management structures discussed above may lead to changes in our management structure. A departure by one or more members of our senior management could have a negative impact on our business, financial condition and results of operations.

Because we have substantial indebtedness, there could be increased risk in investing in our company.

Lenders have fixed dollar claims on our assets that are superior to the claims of stockholders, and we have granted, and may in the future grant, lenders a security interest in our assets in connection with borrowings. In the case of a liquidation event, those lenders would receive proceeds before our stockholders. In addition, borrowings, also known as leverage, magnify the potential for gain or loss on amounts invested and, therefore, increase the risks associated with investing in our securities. Leverage is generally considered a speculative investment technique. If the value of our assets increases, then leverage would cause the NAV attributable to our common stock to increase more than it otherwise would have had we not leveraged. Conversely, if the value of our assets decreases, leverage would cause the NAV attributable to our common stock to decline more than it otherwise would have had we not used leverage. Similarly, any increase in our revenue in excess of interest

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expense on our borrowed funds would cause our net income to increase more than it would without the leverage. Any decrease in our revenue would cause our net income to decline more than it would have had we not borrowed funds and could negatively affect our ability to make distributions on common stock. Our ability to service any debt that we incur will depend largely on our financial performance and will be subject to prevailing economic conditions and competitive pressures. We and, indirectly, our stockholders will bear the cost associated with our leverage activity. If we are not able to service our substantial indebtedness, our business could be harmed materially.

Our Credit Facilities, our 2022 Notes, our 2024 Notes, our 2021 Asset-Backed Notes, and our 2022 Convertible Notes contain financial and operating covenants that could restrict our business activities, including our ability to declare dividend distributions if we default under certain provisions.

As of December 31, 2017, we had no borrowings outstanding under the Wells Facility and the Union Bank Facility. In addition, as of December 31, 2017, we had approximately $190.2 million of indebtedness outstanding incurred by our SBIC subsidiaries, approximately $150.0 million in aggregate principal amount of 2022 Notes, approximately $183.5 million in aggregate principal amount of 2024 Notes, approximately $49.2 million in aggregate principal amount of 2021 Asset-Backed Notes in connection with our $237.4 million debt securitization (the “2014 Debt Securitization”) and approximately $230.0 million in aggregate principal amount of 2022 Convertible Notes.

There can be no assurance that we will be successful in obtaining any additional debt capital on terms acceptable to us or at all. If we are unable to obtain debt capital, then our equity investors will not benefit from the potential for increased returns on equity resulting from leverage to the extent that our investment strategy is successful and we may be limited in our ability to make new commitments or fundings to our portfolio companies.

As a business development company, under the 1940 Act, generally, we are not permitted to incur indebtedness unless immediately after such borrowing we have an asset coverage for total borrowings of at least 200% (i.e., the amount of debt may not exceed 50% of the value of our assets). In addition, we may not be permitted to declare any cash distribution on our outstanding common shares, or purchase any such shares, unless, at the time of such declaration or purchase, we have asset coverage of at least 200% after deducting the amount of such distribution or purchase price. If this ratio declines below 200%, we may not be able to incur additional debt and may need to sell a portion of our investments to repay some debt when it is disadvantageous to do so, and we may not be able to make distributions. The Small Business Credit Availability Act, which was signed into law in March 2018, modifies this section of the 1940 Act and decreases this percentage from 200% to 150% (subject to either stockholder approval or approval of both a majority of the board of directors and a majority of directors who are not interested persons). As a result of this new law, we may be able to incur additional indebtedness subject to relevant approval and disclosure requirements and, therefore, your risk of an investment in us may increase. Rating agencies may also decide to review our credit ratings and those of other business development companies in light of this new law as well as any corresponding changes to asset coverage ratios and consider downgrading such ratings, including a downgrade from an investment grade rating to a non-investment grade rating. Such a downgrade in our credit ratings may adversely affect the Notes and our other securities. See “Supplementary Risk Factors—Risks Related to the Notes—A downgrade, suspension or withdrawal of a credit rating assigned by a rating agency to us or our unsecured debt, if any, or change in the debt markets could cause the liquidity or market value of the Notes to decline significantly” in this prospectus supplement.

As of December 31, 2017 our asset coverage ratio under our regulatory requirements as a business development company was 236.7% excluding our SBIC debentures as a result of our exemptive order from the SEC that allows us to exclude all SBA leverage from our asset coverage ratio and was 204.3% when including all SBA leverage.

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Based on assumed leverage equal to 95.5% of our net assets as of December 31, 2017, our investment portfolio would have been required to experience an annual return of at least 2.9% to cover annual interest payments on our additional indebtedness.

Illustration. The following table illustrates the effect of leverage on returns from an investment in our common stock assuming various annual returns, net of expenses. The calculations in the table below are hypothetical and actual returns may be higher or lower than those appearing below.

Acquisitions or investments that we may pursue could be unsuccessful, consume significant resources and require the incurrence of additional indebtedness.

We regularly consider acquisitions and investments that complement our existing business. These possible acquisitions and investments involve or may involve significant cash expenditures, debt incurrence, operating losses and expenses that could have a material effect on our financial condition and operating results.

In particular, if we incur additional debt, our liquidity and financial stability could be impaired as a result of using a significant portion of available cash or borrowing capacity to finance an acquisition. Moreover, we may face an increase in interest expense or financial leverage if additional debt is incurred to finance an acquisition, which may, among other things, adversely affect our various financial ratios and our compliance with the conditions of our existing indebtedness. In addition, such additional indebtedness may be secured by liens on our assets.

Acquisitions involve numerous other risks, including:

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To the extent we pursue an acquisition that causes us to incur unexpected costs or that fails to generate expected returns, our financial position, results of operations and cash flows may be adversely affected, and our ability to service indebtedness, including our outstanding notes, may be negatively impacted.

In addition, we may fail in our pursuit of an acquisition and, instead, one of our competitors may successfully obtain the target and deprive us of an important opportunity and allow them to grow larger giving them the ability to have a lower cost of capital and competitive advantage in the market (including by being able to offer better pricing and larger loans) and, as a larger company, potentially giving them more valuable equity currency to do other transactions.

The Wells Facility and the Union Bank Facility mature in August 2019 and May 2020, respectively, and any inability to renew, extend or replace our Credit Facilities could adversely impact our liquidity and ability to find new investments or maintain distributions to our stockholders.

As of December 31, 2017, we had two available secured credit facilities, the Wells Facility and the Union Bank Facility, which mature in August 2019 and May 2020, respectively. There can be no assurance that we will be able to renew, extend or replace our Credit Facilities upon maturity on terms that are favorable to us, if at all. Our ability to renew, extend or replace the Credit Facility will be constrained by then-current economic conditions affecting the credit markets. In the event that we are not able to renew, extend or replace either Credit Facility at the time of its maturity, this could have a material adverse effect on our liquidity and ability to fund new investments, our ability to make distributions to our stockholders and our ability to qualify as a RIC.

Regulations governing our operations as a business development company may affect our ability to, and the manner in which, we raise additional capital, which may expose us to risks.

Our business will require a substantial amount of capital. We may acquire additional capital from the issuance of senior securities, including borrowings, securitization transactions or other indebtedness, or the issuance of additional shares of our common stock. However, we may not be able to raise additional capital in the future on favorable terms or at all. We may issue debt securities, other evidences of indebtedness or preferred stock, and we may borrow money from banks or other financial institutions, which we refer to collectively as “senior securities,” up to the maximum amount permitted by the 1940 Act. Under the 1940 Act, we are not permitted to incur indebtedness unless immediately after such borrowing we have an asset coverage for total borrowings of at least 200% (i.e., the amount of debt may not exceed 50% of the value of our assets). In addition, we may not be permitted to declare any cash distribution on our outstanding common shares, or purchase any such shares, unless, at the time of such declaration or purchase, we have asset coverage of at least 200% after deducting the amount of such distribution or purchase price. Our ability to pay distributions or issue additional senior securities would be restricted if our asset coverage ratio were not at least 200%. The Small Business Credit Availability Act, which was signed into law in March 2018, modifies this section of the 1940 Act and decreases this percentage from 200% to 150% (subject to either stockholder approval or approval of both a majority of the board of directors and a majority of directors who are not interested persons). As a result of this new law, we may be able to incur additional indebtedness subject to relevant approval and disclosure requirements and, therefore, your risk of an investment in us may increase. Rating agencies may also decide to review our credit ratings and those of other business development companies in light of this new law as well as any corresponding changes to asset coverage ratios and consider downgrading such ratings, including a downgrade from an investment grade rating to a non-investment grade rating. Such a downgrade in our credit ratings may adversely affect the Notes and our other securities. See “Supplementary Risk Factors—Risks Related to the Notes—A downgrade, suspension or withdrawal of a credit rating assigned by a rating agency to us or our unsecured debt, if any, or change in the debt markets could cause the liquidity or market value of the Notes to decline significantly” in this prospectus supplement.

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If the value of our assets declines, we may be unable to satisfy this test. If that happens, we may be required to liquidate a portion of our investments and repay a portion of our indebtedness at a time when such transaction may be disadvantageous. As a result of issuing senior securities, we would also be exposed to risks associated with leverage, including an increased risk of loss. If we issue preferred stock, the preferred stock would rank “senior” to common stock in our capital structure, preferred stockholders would have separate voting rights and might have rights, preferences, or privileges more favorable than those of our common stockholders and the issuance of preferred stock could have the effect of delaying, deferring, or preventing a transaction or a change of control that might involve a premium price for holders of our common stock or otherwise be in your best interest. It is likely that any senior securities or other indebtedness we issue will be governed by an indenture or other instrument containing covenants restricting our operating flexibility. Additionally, some of these securities or other indebtedness may be rated by rating agencies, and in obtaining a rating for such securities and other indebtedness, we may be required to abide by operating and investment guidelines that further restrict operating and financial flexibility.

To the extent that we are constrained in our ability to issue debt or other senior securities, we will depend on issuances of common stock to finance operations. Other than in certain limited situations such as rights offerings, as a business development company, we are generally not able to issue our common stock at a price below NAV without first obtaining required approvals from our stockholders and our independent directors. If we raise additional funds by issuing more common stock or senior securities convertible into, or exchangeable for, our common stock, then the percentage ownership of our stockholders at that time will decrease, and you might experience dilution. Moreover, we can offer no assurance that we will be able to issue and sell additional equity securities in the future, on favorable terms or at all.

Recently passed legislation may allow us to incur additional leverage.

Historically, as a business development company, under the 1940 Act generally we are not permitted to incur indebtedness unless immediately after such borrowing we have an asset coverage for total borrowings of at least 200% (i.e., the amount of debt may not exceed 50% of the value of our assets). The Small Business Credit Availability Act, which was signed into law in March 2018, modifies this section of the 1940 Act and decreases this percentage from 200% to 150% (subject to either stockholder approval or approval of both a majority of the board of directors and a majority of directors who are not interested persons). As a result of this new law, we may be able to incur additional indebtedness subject to relevant approval and disclosure requirements and, therefore, your risk of an investment in us may increase. Rating agencies may also decide to review our credit ratings and those of other business development companies in light of this new law as well as any corresponding changes to asset coverage ratios and consider downgrading such ratings, including a downgrade from an investment grade rating to a non-investment grade rating. Such a downgrade in our credit ratings may adversely affect the Notes and our other securities. See “Supplementary Risk Factors—Risks Related to the Notes—A downgrade, suspension or withdrawal of a credit rating assigned by a rating agency to us or our unsecured debt, if any, or change in the debt markets could cause the liquidity or market value of the Notes to decline significantly” in this prospectus supplement.

Significant U.S. federal tax legislation was recently enacted and the impact of this new legislation on us and on entities in which we may invest is uncertain.

Significant U.S. federal tax reform legislation was recently enacted that, among many other changes, permanently reduces the maximum federal corporate income tax rate, reduces the maximum individual income tax rate (effective for taxable years 2018 through 2025), restricts the deductibility of business interest expense, changes the rules regarding the calculation of net operating loss deductions that may be used to offset taxable income, and, under certain circumstances, requires accrual method taxpayers to recognize income for U.S. federal income tax purposes no later than the income is taken into account as revenue in an applicable financial statement. The new legislation also makes extensive changes to the U.S. international tax system. The impact of this new legislation on us and on entities in which we may invest is uncertain. Prospective investors are urged to consult their tax advisors regarding the effects of the new legislation on an investment in us.

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Risks Related to Current Economic and Market Conditions

Capital markets may experience periods of disruption and instability and we cannot predict when these conditions will occur. Such market conditions could materially and adversely affect debt and equity capital markets in the United States and abroad, which could have a negative impact on our business, financial condition and results of operations.

The global capital markets have experienced a period of disruption as evidenced by a lack of liquidity in the debt capital markets, write-offs in the financial services sector, the re-pricing of credit risk and the failure of certain major financial institutions. While the capital markets have improved, these conditions could deteriorate again in the future. During such market disruptions, we may have difficulty raising debt or equity capital, especially as a result of regulatory constraints.

Market conditions may in the future make it difficult to extend the maturity of or refinance our existing indebtedness and any failure to do so could have a material adverse effect on our business. The illiquidity of our investments may make it difficult for us to sell such investments if required. As a result, we may realize significantly less than the value at which we have recorded our investments. In addition, significant changes in the capital markets, including the disruption and volatility, have had, and may in the future have, a negative effect on the valuations of our investments and on the potential for liquidity events involving our investments. An inability to raise capital, and any required sale of our investments for liquidity purposes, could have a material adverse impact on our business, financial condition and results of operations.

Various social and political tensions in the United States and around the world, including in the Middle East, Eastern Europe North Korea, and Russia, may continue to contribute to increased market volatility, may have long-term effects on the United States and worldwide financial markets, and may cause further economic uncertainties or deterioration in the United States and worldwide. In addition, uncertainty regarding the United Kingdom referendum decision to leave the European Union (“Brexit”), continuing signs of deteriorating sovereign debt conditions in Europe and an economic slowdown in China create uncertainty that could lead to further disruptions, instability and weakening consumer, corporate and financial confidence. We may in the future have difficulty accessing debt and equity capital markets, and a severe disruption in the global financial markets, deterioration in credit and financing conditions or uncertainty regarding U.S. government spending and deficit levels, Brexit, European sovereign debt, Chinese economic slowdown or other global economic conditions could have a material adverse effect on our business, financial condition and results of operations.

The broader fundamentals of the United States economy remain mixed. In the event that the United States economy contracts, it is likely that the financial results of small to mid-sized companies, like many of our portfolio companies, could experience deterioration or limited growth from current levels, which could ultimately lead to difficulty in meeting their debt service requirements and an increase in defaults. In addition, declines in oil and natural gas prices could adversely affect the credit quality of our debt investments and the underlying operating performance of our equity investments in energy-related businesses. In addition, volatility in the equity markets could impact our portfolio companies’ access to the debt and equity capital markets, which could ultimately limit their ability to grow, satisfy existing financing and other arrangements and impact their ability to perform. Volatility in the equity markets could also impact our ability to liquidate or achieve value from warrants and other equity investments we have in our portfolio companies. Consequently, we can provide no assurance that the performance of certain portfolio companies will not be negatively impacted by economic cycles, industry cycles or other conditions, which could also have a negative impact on our future results.

These market and economic disruptions affect, and these and other similar market and economic disruptions may in the future affect, the U.S. capital markets, which could adversely affect our business and that of our portfolio companies. We cannot predict the duration of the effects related to these or similar events in the future on the United States economy and securities markets or on our investments. We monitor developments and seek to manage our investments in a manner consistent with achieving our investment objective, but there can be no assurance that we will be successful in doing so.

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Risks Related to Our Investments

Our financial results could be negatively affected if a significant portfolio investment fails to perform as expected.

Our total investment in companies may be significant individually or in the aggregate. As a result, if a significant investment in one or more companies fails to perform as expected, our financial results could be more negatively affected and the magnitude of the loss could be more significant than if we had made smaller investments in more companies. The following table shows the fair value of the totals of investments held in portfolio companies at December 31, 2017 that represent greater than 5% of our net assets:

Our financial results could be materially adversely affected if these portfolio companies or any of our other significant portfolio companies encounter financial difficulty and fail to repay their obligations or to perform as expected.

Risks Related to Our Securities

Terms relating to redemption may materially adversely affect your return on any debt securities that we may issue.

If you are holding debt securities issued by the Company and such securities are redeemable at our option, we may choose to redeem your debt securities at times when prevailing interest rates are lower than the interest rate paid on your debt securities. In addition, if you are holding debt securities issued by the Company and such securities are subject to mandatory redemption, we may be required to redeem your debt securities at times when

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prevailing interest rates are lower than the interest rate paid on your debt securities. In this circumstance, you may not be able to reinvest the redemption proceeds in a comparable security at an effective interest rate as high as your debt securities being redeemed.

On October 24, 2017, our Board of Directors approved a redemption of $75.0 million of the outstanding aggregate principal amount of the 2024 Notes, which were redeemed on November 23, 2017. Further, on February 9, 2018, our Board of Directors approved a redemption of $100.0 million of the remaining outstanding aggregate principal amount of the 2024 Notes, which were redeemed on April 2, 2018. We may redeem the remaining 2024 Notes at any time prior to maturity and the 2022 Notes after September 23, 2022 at a redemption price of 100% of the outstanding principal amount thereof plus accrued and unpaid interest payments. If we choose to redeem the 2022 Notes or 2024 Notes when the fair market value of the 2022 Notes or 2024 Notes is above par value, you would experience a loss of any potential premium.

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USE OF PROCEEDS

We estimate that the net proceeds we will receive from the sale of the $75.0 million aggregate principal amount of Notes in this offering will be approximately $72.7 million (or approximately $83.6 million if the underwriters fully exercise their overallotment option) based on a public offering of 100% of par, after deducting the underwriting discount of approximately $2.0 million (or approximately $2.4 million if the underwriters fully exercise their overallotment option) payable by us and estimated offering expenses of approximately $250,000 payable by us.

We expect to use the net proceeds from this offering (i) to fund investments in debt and equity securities in accordance with our investment objective, (ii) to make acquisitions, (iii) to retire certain debt obligations (which may include the 2024 Notes), and (iv) for other general corporate purposes.

As of December 31, 2017, the aggregate principal balance of the 2024 Notes was approximately $183.5 million. On February 9, 2018, our Board of Directors approved a redemption of $100.0 million of the remaining outstanding aggregate principal amount of the 2024 Notes, which were redeemed on April 2, 2018. The 2024 Notes bear interest at a rate of 6.25% per year, payable quarterly and mature, unless earlier repurchased or redeemed, on July 30, 2024.

We intend to seek to invest the net proceeds received in this offering as promptly as practicable after receipt thereof consistent with our investment objective. We anticipate that substantially all of the net proceeds from any offering of our securities will be used as described above within three to six months, depending on market conditions. We anticipate that the remainder will be used for working capital and general corporate purposes, including potential payments or distributions to shareholders. Pending such use, we will invest a portion of the net proceeds of this offering in short-term investments, such as cash and cash equivalents, which we expect will earn yields substantially lower than the interest income that we anticipate receiving in respect of investments in accordance with our investment objective.

The amount of net proceeds may be more or less than the amount described in this preliminary prospectus supplement depending on the amount of Notes we sell in the offering, which will be determined at pricing. To the extent that we receive more than the amount described in this preliminary prospectus supplement, we intend to use the net proceeds for investment in portfolio companies in accordance with our investment objective and strategies and for working capital and general corporate purposes. To the extent we receive less, the amount we have available for such purposes will be reduced.

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SELECTED CONSOLIDATED FINANCIAL DATA

The selected consolidated financial data should be read in conjunction with “Management’s Discussion and Analysis of Financial Condition and Results of Operations,” “Senior Securities” and the consolidated financial statements and related notes included elsewhere herein. The selected balance sheet data as of the end of fiscal year 2017, 2016, 2015, 2014, and 2013 and the financial statement of operations data for fiscal years 2017, 2016, 2015, 2014, and 2013 has been derived from our audited financial statements, which have been audited by PricewaterhouseCoopers LLP, our independent registered public accounting firm, but not all of which are presented in this prospectus supplement. The historical data are not necessarily indicative of results to be expected for any future period.

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The following tables set forth certain quarterly financial information for each of the eight quarters up to and ending December 31, 2017. This information was derived from the Company’s unaudited consolidated financial statements. Results for any quarter are not necessarily indicative of results for the full year or for any future quarter.

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CAPITALIZATION

The following table sets forth (i) our actual capitalization as of December 31, 2017, and (ii) our capitalization as adjusted to give effect to the sale of $75.0 million aggregate principal amount of Notes in this offering (assuming no exercise of the overallotment option), excluding accrued interest, after deducting the underwriting discounts and commissions of approximately $2.0 million payable by us and estimated offering expenses of approximately $250,000 payable by us. You should read this table together with the “Use of Proceeds” section and our statement of assets and liabilities included elsewhere in this prospectus supplement.

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SENIOR SECURITIES

Information about our senior securities is shown in the following table for the periods as of December 31, 2017, 2016, 2015, 2014, 2013, 2012, 2011, 2010, 2009, and 2008. The information as of December 31, 2017, 2016, 2015, 2014, 2013, 2012, 2011 and 2010 has been derived from our audited financial statements for these periods, which have been audited by PricewaterhouseCoopers LLP, our independent registered public accounting firm. The report of PricewaterhouseCoopers LLP on the senior securities table as of December 31, 2017 is attached as an exhibit to the registration statement of which this prospectus is a part. The “—” indicates information that the SEC expressly does not require to be disclosed for certain types of senior securities.

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