MKS INC — Director's Dealing 2010

Mar 12, 2010

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: MKS INSTRUMENTS INC (MKSI)
CIK: 0001049502
Period of Report: 2010-03-10

Reporting Person: STEWART WILLIAM D (V.P. Vacuum Products & PFMC)

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2010-03-10	Common Stock	M	1388	—	Acquired	3779	Direct
2010-03-10	Common Stock	M	2000	—	Acquired	5779	Direct
2010-03-10	Common Stock	F	1054	$19.07	Disposed	4725	Direct

Derivative Transactions

Date	Security	Exercise Price	Code	Shares	A/D	Expiration	Underlying	Ownership
2010-03-10	Restricted Stock Unit	$	M	1388	Disposed		Common Stock (1388)	Direct
2010-03-10	Restricted Stock Unit	$	M	2000	Disposed		Common Stock (2000)	Direct

Footnotes

F1: This transaction was effected pursuant to a Rule 10b5-1 plan previously adopted by the reporting person to satisfy tax withholding obligation.

F2: Each restricted stock unit represents the contingent right to receive one share of common stock of MKS Instruments, Inc.

F3: These RSUs are subject to the achievement of performance criteria determined in the first year of the grant and thereafter vests in equal annual installments over three years.

F4: This number includes 80 shares that were inadvertently omitted from the total amount benefically owned reported on Mr. Stewart's most recent Form 4.

F5: The RSUs vest in equal annual installments over three years.