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                                 SCHEDULE 14A
                                (RULE 14a-101)
                   INFORMATION REQUIRED IN PROXY STATEMENT 
                           SCHEDULE 14A INFORMATION

          Proxy Statement Pursuant to Section 14(a) of the Securities
                    Exchange Act of 1934 (Amendment No.  )
        
Filed by the Registrant [_]

Filed by a Party other than the Registrant [_] 

Check the appropriate box:

[_]  Preliminary Proxy Statement        
                                         
[_]  Confidential, for Use of the Commission Only (as permitted by
     Rule 14a-6(e)(2))                

[_]  Definitive Proxy Statement 

[X]  Definitive Additional Materials 

[_]  Soliciting Material Pursuant to Section 240.14a-11(c) or Section 240.14a-12



                        QUICKTURN DESIGN SYSTEMS, INC.
- --------------------------------------------------------------------------------
               (Name of Registrant as Specified In Its Charter)


- --------------------------------------------------------------------------------
   (Name of Person(s) Filing Proxy Statement, if other than the Registrant)

   
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[X]  No fee required.

[_]  Fee computed on table below per Exchange Act Rules 14a-6(i)(4) and 0-11.

   
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         pursuant to Exchange Act Rule 0-11 (Set forth the amount on which
         the filing fee is calculated and state how it was determined):

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[_]  Fee paid previously with preliminary materials.
     
[_]  Check box if any part of the fee is offset as provided by Exchange
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     was paid previously. Identify the previous filing by registration statement
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Notes:




 
CONTACTS:
 
                                       
   QUICKTURN DESIGN SYSTEMS, INC.            ABERNATHY MACGREGOR FRANK
   Joan Powell                               Pauline Yoshihashi
   Director, Marketing Communications        (213) 630-6550
   (408) 914-6701                            Matt Sherman
   joan@quickturn.com.                       (212) 371-5999
   ----------------------------------------

   
 
FOR IMMEDIATE RELEASE
 
             QUICKTURN SOLICITS PROXIES TO OPPOSE MENTOR'S ATTEMPT
                         TO REPLACE QUICKTURN'S BOARD
 
  SAN JOSE, CALIF. (September 22, 1998) Quickturn Design Systems, Inc.
(Nasdaq: QKTN) sent the following letter to Quickturn stockholders with its
mailing today of proxy materials in connection with the Company's solicitation
of proxies in opposition to Mentor Graphics' proxy materials which were first
mailed to Quickturn stockholders on September 11, 1998.
 
September 22, 1998
 
Dear Fellow Stockholder:
 
       YOUR BOARD URGES YOU TO VOTE QUICKTURN'S ENCLOSED BLUE PROXY CARD
 
  The Board of Directors of Quickturn Design Systems, Inc. is sending you the
enclosed Proxy Statement and BLUE proxy card in opposition to the solicitation
of proxies by Mentor Graphics Corporation to replace your Company's Board with
Mentor's nominees. You may have received proxy material from Mentor seeking
your vote on a GOLD proxy card. Your Board strongly urges you to reject
Mentor's solicitation and to disregard any GOLD proxy cards that you may
receive. YOUR BOARD STRONGLY RECOMMENDS THAT YOU VOTE THE BLUE PROXY CARD
TODAY, AND VOTE AGAINST ALL OF THE MENTOR PROPOSALS.
 
  QUICKTURN'S BOARD HAS DETERMINED THAT THE MENTOR OFFER OF $12.125 PER
QUICKTURN SHARE IS INADEQUATE, DOES NOT REFLECT THE INHERENT VALUE OF THE
COMPANY, AND IS NOT IN THE BEST INTEREST OF QUICKTURN OR ITS STOCKHOLDERS. If
Mentor's nominees are elected to Quickturn's Board, their primary purpose will
be to facilitate Mentor's takeover of Quickturn at what your Board has
determined is an inadequate price.
 
 
            THE CHOICE: QUICKTURN'S FUTURE VS. AN OFFER YOUR BOARD
                        HAS DETERMINED TO BE INADEQUATE
 
  YOUR BOARD STRONGLY BELIEVES THAT QUICKTURN HAS A GREAT FUTURE. Your Board
sees, as we believe Mentor does, the potential for dramatic growth in our key
technologies. We expect total revenues from Quickturn's primary technology,
emulation, to grow at more than 20% per year through 2001, and we expect
revenues from our secondary technology, high-performance simulation, to grow
at more than 40% per year through 2001. We are leaders in both of these
technologies.
 
  YOUR BOARD BELIEVES THAT MENTOR UNDERSTANDS THE SCARCITY VALUE OF
QUICKTURN'S POWERFUL LEADERSHIP POSITION IN THE INDUSTRY. Mentor's numerous
challenges to Quickturn's patents have failed--while Quickturn's patents have
been repeatedly upheld in the courts. We have the patents, we have the
customers, we have the R&D, we have the people, and we have the worldwide
technical support infrastructure. Others have tried to beat us, and they've
failed.

 
  QUICKTURN'S UNRIVALED EXPERIENCE IN EMULATION DELIVERS TECHNICAL PRIMACY.
Your Board believes that Quickturn will generate substantial returns for
Quickturn's stockholders over the next two years and thereafter. The business
prospects for Quickturn for the third and fourth quarters of 1998 continue to
be strong and we are confident that stockholders will find the superior
potential of this Company amply demonstrated in 1999 and 2000, as well.
 
  THIS CONFIDENCE IS BASED UPON THE FOLLOWING FACTORS:
 
  . As the electronics industry makes the transition to deep submicron
    semiconductor processing, we believe the increasing complexity of chip
    design will generate higher demand for verification products;
 
  . Quickturn has invested more than $60 million on research and development
    over the last three years, generating current and future planned products
    such as the Mercury(TM) Design Verification System, which is expected to
    be in full production by year-end;
 
  . Quickturn holds a strong intellectual property position, which includes
    25 issued U.S. patents, 25 pending U.S. patent applications, and numerous
    international patents and application filings;
 
  . Despite the current economic downturn in the Asia/Pacific region,
    Quickturn believes a reinvestment cycle in new design activity in that
    area is imminent, given the competitive forces in the worldwide
    electronics industry; and
 
  . Quickturn is beginning to see some signs of that reinvestment cycle
    commencing in the third quarter and particularly in the fourth quarter of
    this year.
 
  WE BELIEVE MENTOR IS DESPERATELY PURSUING QUICKTURN BECAUSE:
 
  . Quickturn's stock price is temporarily depressed by, among other things,
    the economic slowdown in Asia/Pacific;
 
  . Quickturn's short- and intermediate-term economic prospects continue to
    be strong; and
 
  . The courts have rejected to date every one of Mentor's challenges to our
    patents.
 
            DON'T LET MENTOR STAMPEDE YOU INTO ACCEPTING ITS OFFER
                    VOTE QUICKTURN'S BLUE PROXY CARD TODAY
 
  To further its attempt to take over your company at what the Board has
determined is an inadequate price, Mentor is now asking you and other
stockholders to help it replace your Board with its own handpicked slate of
director nominees. The stated primary purpose of Mentor's nominees is not to
run the company, but to facilitate Mentor's takeover of Quickturn.
 
  Mentor is now attempting an end-run around Quickturn's bylaws in its method
of calling a special meeting of Quickturn stockholders to vote on its slate of
nominees. Our company has rules for calling and holding such meetings. THE
RECORD AND MEETING DATES OF THE SPECIAL MEETING OF STOCKHOLDERS HAVE NOT YET
BEEN SET. We are challenging the validity and legality of Mentor's attempt to
call the special meeting as well as its ability to set the meeting date,
record date, and the place of the special meeting. Each of these matters is
the subject of litigation, which is currently scheduled for early October,
between the Company and Mentor. Subject to the resolution of this litigation,
your Board will schedule the special meeting, if any, in accordance with the
Company's bylaws, which provide for a special meeting date between 90 and 100
days after the receipt and determination of the validity of a request by
stockholders for a special meeting.
 
                                       2

 
            QUICKTURN'S BOARD--YOUR BOARD--IS COMMITTED TO SERVING
                              YOUR BEST INTERESTS
 
  LET'S REVIEW THE FACTS:
 
  . Quickturn's Board of Directors rejected Mentor's offer, and determined
    that Mentor's offer is inadequate, does not reflect the inherent value of
    the company, and is not in the best interests of Quickturn or its
    stockholders;
 
  . Mentor is attempting to call a special meeting of Quickturn stockholders,
    with the primary purpose of removing the Quickturn Board and replacing it
    with its handpicked nominees whose primary objective is to not to run the
    company, but to facilitate Mentor's takeover of Quickturn at what
    Quickturn's Board has determined is an inadequate price; and
 
  . Mentor has sent to you, and is expected to continue to send to you, GOLD
    Proxy Cards in connection with the purported special stockholder meeting.
    Your Board strongly recommends that you disregard and throw away any
    Mentor GOLD Proxy Card sent to you.
 
  Your Board urges Quickturn stockholders to vote against Mentor's attempt to
coerce you to accept its proposal by replacing your Board with Mentor's
handpicked nominees. YOUR BOARD STRONGLY RECOMMENDS THAT YOU VOTE QUICKTURN'S
BLUE PROXY CARD TO SUPPORT YOUR BOARD WHO WILL CONTINUE TO ENSURE THAT YOUR
BEST INTERESTS--NOT MENTOR'S--ARE SERVED. YOUR BOARD URGES YOU TO VOTE AGAINST
THE FOUR MENTOR PROPOSALS ON THE BLUE PROXY CARD.
 
                    VOTE FOR QUICKTURN'S BOARD OF DIRECTORS
                        AND VOTE FOR QUICKTURN'S FUTURE
                         ON THE BLUE PROXY CARD TODAY!
 
  Your Board's rejection of Mentor's offer has reaffirmed its continued
confidence in Quickturn's future and its determination that you, our
stockholders, should be given every opportunity to participate fully in that
future. Your Board of Directors and I greatly appreciate your continued
support and encouragement.
 
  If you have any questions, or need assistance in voting your shares, please
call our proxy solicitor, Morrow & Co. Inc., toll-free, at 1-800-662-5200.
 
                                          On Behalf of the Board of Directors,
 
                                          /s/ Keith R. Lobo
                                          ------------------------
                                          Keith R. Lobo
                                          Chief Executive Officer and
                                           President
 
  Quickturn Design Systems, Inc. is the leading provider of verification
products and time-to-market engineering (TtME(TM)) services for the design of
complex ICs and electronic systems. The company's products are used worldwide
by developers of high-performance computing, multimedia, graphics and
communications systems. Quickturn is headquartered at 55 W. Trimble Road, San
Jose, CA 95131-1013; Telephone: 408/914-6000. For more information, visit the
Quickturn Web site at www.quickturn.com or send e-mail to info@quickturn.com.
 
                                       3

 
           CERTAIN INFORMATION CONCERNING FORWARD-LOOKING STATEMENTS
 
  This letter contains forward-looking statements, including statements
regarding future periods as well as statements regarding the company's
markets. Actual results could differ materially from those described in the
forward-looking statements as a result of factors including, but not limited
to, the following: (i) the company is uncertain whether the recent weakness
experienced in the Asia/Pacific and domestic markets will continue in the
foreseeable future; (ii) product transitions to Quickturn's new Mercury Design
Verification System may be disrupted due to slow market acceptance or due to
disruptions in manufacturing or component availability; (iii) many of the
company's customers order on an as-needed basis and often delay delivery of
firm purchase orders; (iv) the decision of customers to purchase the company's
products involves a lengthy sales cycle which could result, among other
things, in fluctuations of operating results and inventory obsolescence if
expected orders are delayed or not received; (v) the company expects increased
competition, which could result in lost sales or price erosion; (vi) the
company's patents and other proprietary rights may not ensure adequate
protection against competition; (vii) the company serves the electronics and
semiconductor industries, which are noted for rapidly changing needs, there
can be no assurance that Quickturn's product enhancements or new product
introductions will keep pace with or meet those rapidly changing needs or that
new products offered by others will not be superior to those offered by
Quickturn; and (viii) there can be no assurance that Quickturn can retain the
services of key employees and key suppliers upon which the company is
dependent to provide product advances, timely production and high levels of
product quality and reliability.
 
                                       4

 
 
September 22, 1998
 
Dear Fellow Stockholder:
 
       YOUR BOARD URGES YOU TO VOTE QUICKTURN'S ENCLOSED BLUE PROXY CARD
 
  The Board of Directors of Quickturn Design Systems, Inc. is sending you the
enclosed Proxy Statement and BLUE proxy card in opposition to the solicitation
of proxies by Mentor Graphics Corporation to replace your Company's Board with
Mentor's nominees. You may have received proxy material from Mentor seeking
your vote on a GOLD proxy card. Your Board strongly urges you to reject
Mentor's solicitation and to disregard any GOLD proxy cards that you may
receive. YOUR BOARD STRONGLY RECOMMENDS THAT YOU VOTE THE BLUE PROXY CARD
TODAY, AND VOTE AGAINST ALL OF THE MENTOR PROPOSALS.
 
  QUICKTURN'S BOARD HAS DETERMINED THAT THE MENTOR OFFER OF $12.125 PER
QUICKTURN SHARE IS INADEQUATE, DOES NOT REFLECT THE INHERENT VALUE OF THE
COMPANY, AND IS NOT IN THE BEST INTEREST OF QUICKTURN OR ITS STOCKHOLDERS. If
Mentor's nominees are elected to Quickturn's Board, their primary purpose will
be to facilitate Mentor's takeover of Quickturn at what your Board has
determined is an inadequate price.
 
            THE CHOICE: QUICKTURN'S FUTURE VS. AN OFFER YOUR BOARD
                        HAS DETERMINED TO BE INADEQUATE
 
  YOUR BOARD STRONGLY BELIEVES THAT QUICKTURN HAS A GREAT FUTURE. Your Board
sees, as we believe Mentor does, the potential for dramatic growth in our key
technologies. We expect total revenues from Quickturn's primary technology,
emulation, to grow at more than 20% per year through 2001, and we expect
revenues from our secondary technology, high-performance simulation, to grow
at more than 40% per year through 2001. We are leaders in both of these
technologies.
 
  YOUR BOARD BELIEVES THAT MENTOR UNDERSTANDS THE SCARCITY VALUE OF
QUICKTURN'S POWERFUL LEADERSHIP POSITION IN THE INDUSTRY. Mentor's numerous
challenges to Quickturn's patents have failed while Quickturn's patents have
been repeatedly upheld in the courts. We have the patents, we have the
customers, we have the R&D, we have the people, and we have the worldwide
technical support infrastructure. Others have tried to beat us, and they've
failed.
 
  QUICKTURN'S UNRIVALED EXPERIENCE IN EMULATION DELIVERS TECHNICAL PRIMACY.
Your Board believes that Quickturn will generate substantial returns for
Quickturn's stockholders over the next two years and thereafter. The business
prospects for Quickturn for the third and fourth quarters of 1998 continue to
be strong and we are confident that stockholders will find the superior
potential of this Company amply demonstrated in 1999 and 2000, as well.
 

 
  THIS CONFIDENCE IS BASED UPON THE FOLLOWING FACTORS:
 
  . As the electronics industry makes the transition to deep submicron
    semiconductor processing, we believe the increasing complexity of chip
    design will generate higher demand for verification products;
 
  . Quickturn has invested more than $60 million on research and development
    over the last three years, generating current and future planned products
    such as the Mercury(TM) Design Verification System, which is expected to
    be in full production by year-end;
 
  . Quickturn holds a strong intellectual property position, which includes
    25 issued U.S. patents, 25 pending U.S. patent applications, and numerous
    international patents and application filings;
 
  . Despite the current economic downturn in the Asia/Pacific region,
    Quickturn believes a reinvestment cycle in new design activity in that
    area is imminent, given the competitive forces in the worldwide
    electronics industry; and
 
  . Quickturn is beginning to see some signs of that reinvestment cycle
    commencing in the third quarter and particularly in the fourth quarter of
    this year.
 
  WE BELIEVE MENTOR IS DESPERATELY PURSUING QUICKTURN BECAUSE:
 
  . Quickturn's stock price is temporarily depressed by, among other things,
    the economic slowdown in Asia/Pacific;
 
  . Quickturn's short- and intermediate-term economic prospects continue to
    be strong; and
 
  . The courts have rejected to date every one of Mentor's challenges to our
    patents.
 
            DON'T LET MENTOR STAMPEDE YOU INTO ACCEPTING ITS OFFER
                    VOTE QUICKTURN'S BLUE PROXY CARD TODAY
 
  To further its attempt to take over your company at what the Board has
determined is an inadequate price, Mentor is now asking you and other
stockholders to help it replace your Board with its own handpicked slate of
director nominees. The stated primary purpose of Mentor's nominees is not to
run the company, but to facilitate Mentor's takeover of Quickturn.
 
  Mentor is now attempting an end-run around Quickturn's bylaws in its method
of calling a special meeting of Quickturn stockholders to vote on its slate of
nominees. Our company has rules for calling and holding such meetings. THE
RECORD AND MEETING DATES OF THE SPECIAL MEETING OF STOCKHOLDERS HAVE NOT YET
BEEN SET. We are challenging the validity and legality of Mentor's attempt to
call the special meeting as well as its ability to set the meeting date,
record date, and the place of the special meeting. Each of these matters is
the subject of litigation, which is currently scheduled for early October,
between the Company and Mentor. Subject to the resolution of this litigation,
your Board will schedule the special meeting, if any, in accordance with the
Company's bylaws, which provide for a special meeting date between 90 and 100
days after the receipt and determination of the validity of a request by
stockholders for a special meeting.
 
                                       2

 
            QUICKTURN'S BOARD--YOUR BOARD--IS COMMITTED TO SERVING
                              YOUR BEST INTERESTS
 
  LET'S REVIEW THE FACTS:
 
  . Quickturn's Board of Directors rejected Mentor's offer, and determined
    that Mentor's offer is inadequate, does not reflect the inherent value of
    the company, and is not in the best interests of Quickturn or its
    stockholders;
 
  . Mentor is attempting to call a special meeting of Quickturn stockholders,
    with the primary purpose of removing the Quickturn Board and replacing it
    with its handpicked nominees whose primary objective is to not to run the
    company, but to facilitate Mentor's takeover of Quickturn at what
    Quickturn's Board has determined is an inadequate price; and
 
  . Mentor has sent to you, and is expected to continue to send to you, GOLD
    Proxy Cards in connection with the purported special stockholder meeting.
    Your Board strongly recommends that you disregard and throw away any
    Mentor GOLD Proxy Card sent to you.
 
  Your Board urges Quickturn stockholders to vote against Mentor's attempt to
coerce you to accept its proposal by replacing your Board with Mentor's
handpicked nominees. YOUR BOARD STRONGLY RECOMMENDS THAT YOU VOTE QUICKTURN'S
BLUE PROXY CARD TO SUPPORT YOUR BOARD WHO WILL CONTINUE TO ENSURE THAT YOUR
BEST INTERESTS--NOT MENTOR'S--ARE SERVED. YOUR BOARD URGES YOU TO VOTE AGAINST
THE FOUR MENTOR PROPOSALS ON THE BLUE PROXY CARD.
 
                    VOTE FOR QUICKTURN'S BOARD OF DIRECTORS
                        AND VOTE FOR QUICKTURN'S FUTURE
                         ON THE BLUE PROXY CARD TODAY!
 
  Your Board's rejection of Mentor's offer has reaffirmed its continued
confidence in Quickturn's future and its determination that you, our
stockholders, should be given every opportunity to participate fully in that
future. Your Board of Directors and I greatly appreciate your continued
support and encouragement.
 
  If you have any questions, or need assistance in voting your shares, please
call our proxy solicitor, Morrow & Co. Inc., toll-free, at 1-800-662-5200.
 
                                          On Behalf of the Board of Directors,
 
                                          /s/ Keith R. Lobo
                                          -----------------------
                                          Keith R. Lobo
                                          Chief Executive Officer and
                                           President
 
                                       3

 
           CERTAIN INFORMATION CONCERNING FORWARD-LOOKING STATEMENTS
 
  This letter contains forward-looking statements, including statements
regarding future periods as well as statements regarding the company's
markets. Actual results could differ materially from those described in the
forward-looking statements as a result of factors including, but not limited
to, the following: (i) the company is uncertain whether the recent weakness
experienced in the Asia/Pacific and domestic markets will continue in the
foreseeable future; (ii) product transitions to Quickturn's new Mercury Design
Verification System may be disrupted due to slow market acceptance or due to
disruptions in manufacturing or component availability; (iii) many of the
company's customers order on an as-needed basis and often delay delivery of
firm purchase orders; (iv) the decision of customers to purchase the company's
products involves a lengthy sales cycle which could result, among other
things, in fluctuations of operating results and inventory obsolescence if
expected orders are delayed or not received; (v) the company expects increased
competition, which could result in lost sales or price erosion; (vi) the
company's patents and other proprietary rights may not ensure adequate
protection against competition; (vii) the company serves the electronics and
semiconductor industries, which are noted for rapidly changing needs, there
can be no assurance that Quickturn's product enhancements or new product
introductions will keep pace with or meet those rapidly changing needs or that
new products offered by others will not be superior to those offered by
Quickturn; and (viii) there can be no assurance that Quickturn can retain the
services of key employees and key suppliers upon which the company is
dependent to provide product advances, timely production and high levels of
product quality and reliability.
 
                                       4