FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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(Print or Type Responses)

1. Name and Address of Reporting Person * EMERSON ELECTRIC CO   2. Issuer Name and Ticker or Trading Symbol MKS INSTRUMENTS INC [MKSI] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director __X__ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 8000 W. FLORISSANT AVE. 3. Date of Earliest Transaction (Month/Day/Year) 03/29/2006 (Street) ST LOUIS, MO 63136 4. If Amendment, Date Original Filed(Month/Day/Year) 6. Individual or Joint/Group Filing(Check Applicable Line) ___ Form filed by One Reporting Person _X_ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned

1.Title of Security (Instr. 3) 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock 03/29/2006   S   15,000 D $ 23.2516 (1) 7,491,711 I Through a subsidiary (2) Common Stock 03/30/2006   S   15,000 D $ 23.1556 (3) 7,476,711 I Through a subsidiary (2) Common Stock               1,065,182 D (4)

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 3)

2. Conversion or Exercise Price of Derivative Security

3. Transaction Date (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

4. Transaction Code (Instr. 8)

5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5)

6. Date Exercisable and Expiration Date (Month/Day/Year)

7. Title and Amount of Underlying Securities (Instr. 3 and 4)

8. Price of Derivative Security (Instr. 5)

9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)

10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)

11. Nature of Indirect Beneficial Ownership (Instr. 4)

Code

V

(A)

(D)

Date Exercisable

Expiration Date

Title

Amount or Number of Shares

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
EMERSON ELECTRIC CO 8000 W. FLORISSANT AVE. ST LOUIS, MO 63136		X
ASTEC AMERICA INC 5810 VAN ALLEN WAY CARLSBAD, CA 92008		X

Signatures

/s/ Harley M. Smith, Assistant Secretary for Emerson Electric Co.		03/31/2006
**Signature of Reporting Person		Date
/s/ Harley M. Smith, Secretary for Astec America Inc.		03/31/2006
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	The sales were effected in multiple transactions, at varying prices, on March 29, 2006, as follows: 2,248 shares at $23.23; 1,000 at $23.24; 6,206 at $23.25; 3,200 at $23.26; and 2,346 at $23.27. The weighted average sales price for these transactions was $23.2516 per share.
(2)	The reported securities are owned directly by Astec America Inc. The Reporting Person is the ultimate parent company of Astec America Inc.
(3)	The sales were effected in multiple transactions, at varying prices, on March 30, 2006, as follows: 100 shares at $23.07; 100 at $23.08; 300 at $23.09; 1,300 at $23.10; 700 at $23.11; 1,700 at $23.12; 1,100 at $23.13; 700 at $23.14; 2,600 at $23.15; 1,500 at $23.16; 900 at $23.17; 900 at $23.18; 412 at $23.19; 688 at $23.20; 700 at $23.21; 100 at $23.22; 200 at $23.23; 400 at $23.24; 200 at $23.26; 100 at $23.27; 100 at $23.29; and 200 at $23.30. The weighted average sales price for these transactions was $23.1556 per share.
(4)	The reported securities are owned directly by Emerson Electric Co.
Remarks: See Exhibit 99.1 - Joint Filer Information

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