MKS Instruments Inc (MKSI)

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Dear shareholder:

You are cordially invited to attend the Annual Meeting of Shareholders of MKS Instruments, Inc. to be held on Monday, May 5, 2008, at 10:00 a.m. at the Wyndham Boston Andover Hotel, 123 Old River Road, Andover, Massachusetts 01810.

The enclosed notice of Annual Meeting and proxy statement describe the business to be transacted at the Annual Meeting and provide additional information about us that you should know when voting your shares. The principal business at the Annual Meeting will be to elect Class III Directors and ratify the selection of the independent registered public accounting firm for fiscal 2008.

Whether or not you plan to attend the Annual Meeting, please complete, date, sign and return your Proxy Card promptly in the enclosed envelope, which requires no postage if mailed in the United States. If you attend the Annual Meeting, you may vote in person if you wish, even if you have previously returned your Proxy Card.

On behalf of MKS, I would like to express our appreciation for your continued interest in our company.

Sincerely,

LEO BERLINGHIERI
Chief Executive Officer and President