MKS INC — Director's Dealing 2012

Mar 1, 2012

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: MKS INSTRUMENTS INC (MKSI)
CIK: 0001049502
Period of Report: 2012-02-28

Reporting Person: STEWART WILLIAM D (VP/GM, Vacuum Products)

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2012-02-28	Common Stock	M	1446.079	—	Acquired	1446.079	Direct
2012-02-28	Common Stock	M	1018	—	Acquired	2464.079	Direct
2012-02-28	Common Stock	F	767	$30.63	Disposed	1697.079	Direct

Derivative Transactions

Date	Security	Exercise Price	Code	Shares	A/D	Expiration	Underlying	Ownership
2012-02-28	Restricted Stock Unit	$	M	1446.079	Disposed		Common Stock (1446.079)	Direct
2012-02-28	Restricted Stock Unit	$	M	1018	Disposed		Common Stock (1018)	Direct

Holdings (Non-Derivative)

Security	Shares	Ownership
Common Stock	0.552	Indirect

Footnotes

F1: Each restricted stock unit represents the contingent right to receive one share of common stock of MKS Instruments, Inc.

F2: This transaction was effected pursuant to a Rule 10b5-1 trading plan previously adopted by the reporting person.

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