
<PAGE>

                                                                  EXHIBIT (A)(7)

                             SUMMARY ADVERTISEMENT
 
  This announcement is neither an offer to purchase nor a solicitation of an
offer to sell Shares. The Offer is made solely by the Offer to Purchase dated
January 22, 1999 and the related Letter of Transmittal, and is being made to
all holders of Shares. Purchaser is not aware of any state where the making of
the Offer is prohibited by administrative or judicial action pursuant to any
valid state statute. If Purchaser becomes aware of any valid state statute
prohibiting the making of the Offer or the acceptance of Shares pursuant
thereto, Purchaser will make a good faith effort to comply with such state
statute. If, after such good faith effort, Purchaser cannot comply with such
state statute, the Offer will not be made to (nor will tenders be accepted
from or on behalf of) the holders of Shares in such state. In any jurisdiction
where the securities, blue sky or other laws require the Offer to be made by a
licensed broker or dealer, the Offer shall be deemed to be made on behalf of
Purchaser by one or more registered brokers or dealers licensed under the laws
of such jurisdiction.
 
                     Notice of 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
 
  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"), is
offering 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 thereon, 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 constitute the "Offer"). Following
the Offer, Purchaser intends to effect the Merger described below. Parent is a
wholly owned subsidiary of STEAG Aktiengesellschaft, a corporation organized
under the laws of the Federal Republic of Germany.
 
 
    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.
 
 
  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 below, 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 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 and not withdrawn
by the Expiration Date (as defined below)).
 
  The Offer is being made pursuant to an Agreement and Plan of Merger dated as
of January 18, 1999 (the "Merger Agreement") among Parent, Purchaser and the
Company. The Merger Agreement provides that, among other things, subject to
the terms and conditions in the Merger Agreement, and in accordance with the
Delaware General Corporation Law and California General Corporation Law (the
"CGCL"), Purchaser will be merged with and into the Company (the "Merger").
Following consummation of the Merger, the Company will continue as the
surviving corporation and will become a wholly owned subsidiary of Parent. At
the effective time of the Merger (the "Effective Time"), each issued and
outstanding Share immediately prior to the Effective Time (other than (a)
Shares held by any subsidiary of the Company, (b) each Share owned by Parent
or Purchaser, including Shares purchased by Purchaser pursuant to the Offer,
and (c) Shares held by shareholders who have demanded and perfected, and have
not withdrawn or otherwise lost, dissenters' rights, if any, under the CGCL)
will be cancelled and converted automatically into the right to receive $5.50
in cash, or any higher price that may be paid per Share in the Offer, without
interest.
<PAGE>
 
  THE BOARD OF DIRECTORS OF THE COMPANY HAS UNANIMOUSLY APPROVED THE MERGER
AGREEMENT AND THE TRANSACTIONS CONTEMPLATED THEREBY (INCLUDING THE OFFER AND
THE MERGER), HAS DETERMINED THAT THE MERGER AGREEMENT AND THE TRANSACTIONS
CONTEMPLATED THEREBY (INCLUDING THE OFFER AND THE MERGER) ARE FAIR TO, AND IN
THE BEST INTERESTS OF, THE COMPANY AND THE SHAREHOLDERS OF THE COMPANY, AND
RECOMMENDS THAT SHAREHOLDERS ACCEPT THE OFFER AND TENDER THEIR SHARES PURSUANT
TO THE OFFER.
 
  Simultaneously with entering into the Merger Agreement, and as an inducement
to Parent and Purchaser to enter into the Merger Agreement, the Company
entered into a Stock Option Agreement with Parent and Purchaser, dated as of
January 18, 1999 (the "Stock Option Agreement"). Pursuant to the Stock Option
Agreement, the Company granted to Purchaser an irrevocable option (the "Stock
Option") to purchase up to the number of Shares (the "Option Shares") that,
when added to the number of Shares owned by Purchaser and its affiliates
following the consummation of the Offer, would constitute 90% of the Shares
then outstanding (assuming the issuance of the Option Shares), at a cash
purchase price per Option Share equal to $5.50, subject to the terms and
conditions in the Stock Option Agreement, including, without limitation, (i)
that not less than 80% of the Shares then outstanding have been tendered upon
the Expiration Date, and (ii) that the number of Shares to be issued
thereunder shall not exceed the number of authorized Shares available for
issuance.
 
  If the Stock Option is exercised by Purchaser (resulting in Purchaser
acquiring 90% or more of the Shares then outstanding) or Purchaser otherwise
acquires 90% of the Shares then outstanding, Parent will be able to effect a
short-form merger without a vote of the Company's shareholders under the CGCL,
subject to the terms and conditions of the Merger Agreement. Purchaser
currently intends to effect a short-form merger if it is able to do so.
 
  For purposes of the Offer, Purchaser will be deemed to have accepted for
payment, and thereby purchased, Shares validly tendered and not properly
withdrawn as, if and when Purchaser gives oral or written notice to
BankBoston, N.A. (the "Depositary") of Purchaser's acceptance for payment of
such Shares pursuant to the Offer. Upon the terms and subject to the
conditions of the Offer, payment for Shares accepted for payment pursuant to
the Offer will be made by deposit of the purchase price therefor with the
Depositary, which will act as agent for tendering shareholders for the purpose
of receiving payments from Purchaser and transmitting such payments to
tendering shareholders whose Shares have been accepted for payment. Under no
circumstances will interest on the purchase price for Shares be paid,
regardless of any extension of the Offer or delay in making such payment. 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 such Shares (the "Share Certificates") or timely
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) pursuant to the procedures set forth in Section 3 of the Offer to
Purchase, (ii) the Letter of Transmittal (or a 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 under the Letter of
Transmittal.
 
  Purchaser expressly reserves the right, in its sole discretion (subject to
the terms and conditions of the Merger Agreement), at any time and from time
to time, to extend for any reason the period of time during which the Offer is
open, including the occurrence of any condition specified in Section 14 of the
Offer to Purchase, by giving oral or written notice of such extension to the
Depositary. Any such extension will be followed as promptly as practicable by
public announcement thereof, such announcement to be made no later than 9:00
a.m., New York City time, on the next business day after the previously
scheduled Expiration Date of the Offer. During any such extension, all Shares
previously tendered and not withdrawn will remain subject to the Offer and to
the rights of tendering shareholders to withdraw their Shares.
 
  The term "Expiration Date" means 12:00 Midnight, New York City time, on
Friday, February 19, 1999, unless and until Purchaser shall have extended the
period of time during which the Offer is open, in which event the term
"Expiration Date" shall mean the latest time and date at which the Offer, as
so extended by Purchaser, will expire.
 
  Tenders of Shares made pursuant to the Offer are irrevocable except that
such Shares may be withdrawn at any time prior to the Expiration Date and,
unless theretofore accepted for payment by Purchaser pursuant to the Offer,
may also be withdrawn at any time after Monday, March 22, 1999. For the
withdrawal to be effective, a written, telegraphic or facsimile transmission
notice of withdrawal must be timely received by the Depositary at one of its
addresses set forth on the back cover page of the Offer to Purchase. Any such
notice of withdrawal must specify the name of the person who tendered the
Shares to be withdrawn, the number of Shares to be withdrawn and the name of
the registered holder of such Shares, if different from that of the person who
tendered such Shares. If Share Certificates evidencing Shares to be withdrawn
have been delivered or otherwise identified to the Depositary, then, prior to
the physical release of such Share Certificates, the serial numbers shown on
such Share Certificates must be submitted to the Depositary and the
signature(s) on the notice of withdrawal must be guaranteed by an Eligible
Institution (as defined in Section 3 of the Offer to Purchase), unless such
Shares have been tendered for the account of an Eligible Institution. If
Shares have been tendered pursuant to the procedure for book-entry transfer as
set forth in Section 3 of the Offer to Purchase, any notice of withdrawal must
specify the name and number of the account at the Book-Entry Transfer Facility
to be credited with the withdrawn Shares and must otherwise comply with such
Book-Entry Transfer Facility's procedures. All questions as to the form and
validity (including the time of receipt) of any notice of withdrawal will be
determined by Purchaser, in its sole discretion, whose determination will be
final and binding.
 
  The information required to be disclosed by Rule 14d-6(e)(1)(vii) of the
General Rules and Regulations under the Securities Exchange Act of 1934, as
amended, is contained in the Offer to Purchase and is incorporated herein by
reference.
<PAGE>
 
  The Company has provided Purchaser with the Company's shareholder list and
security position listings for the purpose of disseminating the Offer to
holders of Shares. The Offer to Purchase and the related Letter of Transmittal
will be mailed to record holders of Shares whose names appear on the Company's
shareholder list and will be furnished to brokers, dealers, commercial banks,
trust companies and similar persons whose names, or the names of whose
nominees, appear on the shareholder list or, if applicable, who are listed as
participants in a clearing agency's security position listing for subsequent
transmittal to beneficial owners of Shares.
 
  THE OFFER TO PURCHASE AND THE RELATED LETTER OF TRANSMITTAL CONTAIN
IMPORTANT INFORMATION WHICH SHOULD BE READ BEFORE ANY DECISION IS MADE WITH
RESPECT TO THE OFFER.
 
  Questions and requests for assistance or for additional copies of the Offer
to Purchase and the related Letter of Transmittal and other tender offer
materials may be directed to the Information Agent as set forth below, and
copies will be furnished promptly at Purchaser's expense. Neither Purchaser
nor Parent nor any officer, director, stockholder, agent or other
representative will pay any fees or commissions to brokers, dealers or other
persons (other than the Depositary and the Information Agent, as described in
the Offer to Purchase) for soliciting tenders of Shares pursuant to the Offer.
 
                    The Information Agent for the Offer is:
 
[LOGO OF CIC]       CORPORATE INVESTOR COMMUNICATIONS, INC.
             111 Commerce Road - Carlstadt, New Jersey 07072-2586
 
                 Banks and Brokers call collect (800) 346-7885
                   All others call toll free (888) 206-3388



January 22, 1999
