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                                                                  EXHIBIT (A)(4)
 
                          Offer to Purchase for Cash
                    All Outstanding Shares of Common Stock
 
                                      of
 
                              AG Associates, Inc.
 
                                      at
 
                              $5.50 Net Per Share
 
                                      by
 
                          MIG Acquisition Corporation
 
                         a wholly owned subsidiary of
 
                         STEAG Electronic Systems GmbH
 
    THE OFFER, WITHDRAWAL RIGHTS AND PRORATION PERIOD WILL EXPIRE AT 12:00
 MIDNIGHT, NEW YORK CITY TIME, ON FRIDAY, FEBRUARY 19, 1999, UNLESS THE OFFER
                                 IS EXTENDED.
 
 
                                                               January 22, 1999
 
To Brokers, Dealers, Commercial Banks,
 Trust Companies and Other Nominees:
 
  We have been appointed by MIG Acquisition Corporation, a Delaware
corporation ("Purchaser") and a wholly owned subsidiary of STEAG Electronic
Systems GmbH, a corporation organized under the laws of the Federal Republic
of Germany ("Parent"), to act as Information Agent in connection with
Purchaser's offer to purchase all outstanding shares of common stock, without
par value (the "Shares"), of AG Associates, Inc., a California corporation
(the "Company"), at a price of $5.50 per Share, net to the seller in cash,
without interest, upon the terms and subject to the conditions set forth in
Purchaser's Offer to Purchase, dated January 22, 1999 (the "Offer to
Purchase"), and the related Letter of Transmittal (which, as amended or
supplemented from time to time, together with the Offer to Purchase,
constitute the "Offer") enclosed herewith. Please furnish copies of the
enclosed materials to those of your clients for whose accounts you hold Shares
registered in your name or in the name of your nominee.
 
  The Offer is conditioned upon, among other things, (i) there being validly
tendered and not withdrawn prior to the expiration of the Offer such number of
Shares which would constitute not less than 90% of the Shares then outstanding
(the "Minimum Condition"), and (ii) the expiration or termination of any
applicable waiting periods under the Hart-Scott-Rodino Antitrust Improvements
Act of 1976, as amended. The Offer also is subject to the other terms and
conditions described in the Offer to Purchase.
 
  In the event that more than 50% of the Shares then outstanding are tendered
pursuant to the Offer and not withdrawn, but less than 90% of the Shares then
outstanding are acquired by Purchaser pursuant to the Offer and the Stock
Option described in the Offer to Purchase, Purchaser will waive the Minimum
Condition and amend the Offer to reduce the number of Shares subject to the
Offer to 3,095,294 Shares or such greater or lesser number of Shares as equals
49.9% of the Shares then outstanding (the "Revised Minimum Number") and, if a
greater number of Shares is tendered into the Offer and not withdrawn,
purchase, on a pro rata basis, the Revised Minimum Number of Shares (it being
understood that Purchaser shall not in any event be required to accept for
payment, or pay for, any shares if less than the Revised Minimum Number of
Shares are tendered pursuant to the Offer and not withdrawn at the expiration
of the Offer).
 
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  Enclosed for your information and for forwarding to your clients for whom
you hold Shares registered in your name or in the name of your nominee, or who
hold Shares registered in their own names, are copies of the following
documents:
 
    1. Offer to Purchase, dated January 22, 1999;
 
    2. Letter of Transmittal to tender Shares for your use and for the
  information of your clients. Facsimile copies of the Letter of Transmittal
  may be used to tender Shares;
 
    3. Notice of Guaranteed Delivery to be used to accept the Offer if
  certificates for Shares are not immediately available or time will not
  permit all required documents to reach BankBoston, N.A. (the "Depositary")
  by the Expiration Date (as defined in the Offer to Purchase) or if the
  procedure for book-entry transfer cannot be completed by the Expiration
  Date;
 
    4. A letter to shareholders of the Company from Dr. Arnon Gat, Chief
  Executive Officer and Chairman of the Company, together with the
  Solicitation/Recommendation Statement on Schedule 14D-9 filed with the
  Securities and Exchange Commission by the Company;
 
    5. A letter which may be sent to your clients for whose accounts you hold
  Shares registered in your name or in the name of your nominee, with space
  provided for obtaining such clients' instructions with regard to the Offer;
 
    6. Guidelines for Certification of Taxpayer Identification Number on
  Substitute Form W-9; and
 
    7. A return envelope addressed to the Depositary.
 
  WE URGE YOU TO CONTACT YOUR CLIENTS AS PROMPTLY AS POSSIBLE. PLEASE NOTE
THAT THE OFFER AND WITHDRAWAL RIGHTS EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY
TIME, ON FRIDAY, FEBRUARY 19, 1999, UNLESS THE OFFER IS EXTENDED.
 
  In all cases, payment for Shares tendered and accepted for payment pursuant
to the Offer will be made only after timely receipt by the Depositary of (i)
the certificates evidencing the tendered Shares (or a confirmation of a book-
entry transfer of such Shares into the Depositary's account at the Book-Entry
Transfer Facility (as defined in the Offer to Purchase)), (ii) a Letter of
Transmittal (or facsimile thereof), properly completed and duly executed, with
any required signature guarantees or, in the case of a book-entry transfer, an
Agent's Message (as defined in the Offer to Purchase) and (iii) any other
documents required by the Letter of Transmittal.
 
  If holders of Shares wish to tender, but cannot deliver their certificates
or other required documents or cannot comply with the procedures for book-
entry transfer prior to the expiration of the Offer, a tender may be effected
by following the guaranteed delivery procedures described in "Section 3.
Procedures for Accepting the Offer and Tendering Shares" of the Offer to
Purchase.
 
  Neither Purchaser nor Parent will pay any fees or commissions to any broker,
dealer or other person (other than the Depositary and the Information Agent,
as described in the Offer) in connection with the solicitation of tenders of
Shares pursuant to the Offer. However, Purchaser will, upon request, reimburse
you for customary mailing and handling expenses incurred by you in forwarding
any of the enclosed materials to your clients. Purchaser will pay or cause to
be paid any stock transfer taxes payable with respect to the transfer of
Shares to it, except as otherwise provided in Instruction 6 of the Letter of
Transmittal. Backup tax withholding at a rate of 31% may be required, however,
unless the required tax identification information is provided. See "Important
Tax Information" contained in the Letter of Transmittal.
 
 
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  Any inquiries you may have with respect to the Offer should be addressed to,
and additional copies of the enclosed material may be obtained by contacting
the undersigned at the address and telephone number set forth on the back
cover page of the Offer to Purchase.
 
                                          Very truly yours,
 
                                          Corporate Investor Communications,
                                           Inc.
 
  NOTHING CONTAINED HEREIN OR IN THE ENCLOSED DOCUMENTS SHALL RENDER YOU OR
ANY OTHER PERSON THE AGENT OF PARENT, PURCHASER, THE COMPANY, THE INFORMATION
AGENT OR THE DEPOSITARY, OR ANY AFFILIATE OF ANY OF THEM, OR AUTHORIZE YOU OR
ANY OTHER PERSON TO USE ANY DOCUMENT OR TO MAKE ANY STATEMENT ON BEHALF OF ANY
OF THEM IN CONNECTION WITH THE OFFER OTHER THAN THE ENCLOSED DOCUMENTS AND THE
STATEMENTS CONTAINED THEREIN.
 
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1404-LT-99
