MKS INC — Director's Dealing 2012

Apr 3, 2012

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: MKS INSTRUMENTS INC (MKSI)
CIK: 0001049502
Period of Report: 2012-04-02

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

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2012-04-02	Common Stock	M	5592.158	—	Acquired	12841.237	Direct
2012-04-02	Common Stock	M	6037.097	—	Acquired	18878.334	Direct
2012-04-02	Common Stock	F	3617	$29.70	Disposed	15261.334	Direct

Derivative Transactions

Date	Security	Exercise Price	Code	Shares	A/D	Expiration	Underlying	Ownership
2012-04-02	Restricted Stock Unit	$	M	5592.158	Disposed		Common Stock (5592.158)	Direct
2012-04-02	Restricted Stock Unit	$	M	6037.097	Disposed		Common Stock (6037.097)	Direct

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: Mr. Stewart resigned from the Company on April 2, 2012. Upon Mr. Stewart's resignation for good cause, 100% of unvested RSUs vest per agreement with Company.

F4: 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.

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