MKS INC — Director's Dealing 2010

Mar 29, 2010

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: MKS INSTRUMENTS INC (MKSI)
CIK: 0001049502
Period of Report: 2010-03-25

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

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2010-03-25	Common Stock	M	1875	$14.72	Acquired	8914	Direct
2010-03-25	Common Stock	S	8914	$19.50	Disposed	0	Direct

Derivative Transactions

Date	Security	Exercise Price	Code	Shares	A/D	Expiration	Underlying	Ownership
2010-03-25	Stock Option (Right to Buy)	$14.72	M	1875	Disposed	2014-07-30	Common Stock (1875)	Direct

Footnotes

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

F2: 25% after first year, 6.25% each quater thereafter - total 4 years.