MKS INC — Director's Dealing 2010

May 11, 2010

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: MKS INSTRUMENTS INC (MKSI)
CIK: 0001049502
Period of Report: 2010-05-03

Reporting Person: Amon Cristina (Director)

Non-Derivative Transactions

Date	Security	Code	Shares	Price	A/D	Holdings After	Ownership
2010-05-03	Common Stock	A	6000	—	Acquired	20110	Direct
2010-05-07	Common Stock	M	556	—	Acquired	20666	Direct

Derivative Transactions

Date	Security	Exercise Price	Code	Shares	A/D	Expiration	Underlying	Ownership
2010-05-07	Restricted Stock Unit	$	M	556	Disposed		Common Stock (556)	Direct

Footnotes

F1: This RSU grant fully vests on the day prior to the first annual meeting of shareholders following the date of grant (or if no such meeting is held within 13 months after the date of grant, on the 13 month anniversary of the date of grant).

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

F3: vests in 12 equal quarterly installments over a three-year period.