Exhibit 99.1

                    TERMINATION AGREEMENT AND MUTUAL RELEASE


         This  TERMINATION  AGREEMENT  AND MUTUAL  RELEASE dated as of March 12,
2002 (this "Agreement") is made and entered into by and among Synopsys,  Inc., a
Delaware corporation ("Parent"),  Oak Merger Corporation, a Delaware corporation
("Merger Sub") and wholly-owned  subsidiary of Parent, and IKOS Systems, Inc., a
Delaware  corporation  (the "Company").  Parent,  Merger Sub and the Company are
collectively  referred to herein as the  "Parties"  and each  individually  as a
"Party."  Capitalized  terms used but not defined  herein shall have the meaning
set forth in the Merger Agreement (as defined below).

                                    Recitals

         WHEREAS the Parties  entered into an  Agreement  and Plan of Merger and
Reorganization  dated as of July 2, 2001 (as  amended,  the "Merger  Agreement")
pursuant to which,  subject to the terms and conditions  stated therein,  Merger
Sub was to merge with and into the  Company  and the  Company was to continue as
the surviving corporation and a wholly-owned subsidiary of Parent;

         WHEREAS  contemporaneously  with the execution of the Merger Agreement,
Parent,  Company and certain  stockholders  or employees of the Company  entered
into Company Voting Agreements (the "Voting Agreements");

         WHEREAS  on  December  7,  2001  Fresno   Corporation   ("Fresno"),   a
wholly-owned subsidiary of Mentor Graphics Corporation  ("Mentor"),  commenced a
cash tender  offer to acquire  all of the  outstanding  shares of the  Company's
common stock for $11.00 cash per share (the "Mentor Tender Offer");

         WHEREAS on January 16, 2002 as part of the Mentor Tender Offer,  Mentor
delivered  to  the  Company  a  proposed   Agreement  and  Plan  of  Merger  and
Reorganization  by and among  Mentor,  Fresno and the Company  providing,  among
other  things,  that Mentor would amend the Mentor Tender Offer to eliminate the
"Termination  Fee Condition" and that the Company and Mentor  promptly take such
actions as required to cause the dismissal  with  prejudice of the lawsuits (the
"Deal  Related  Litigation")  currently  pending  before the  Delaware  Court of
Chancery  and the United  States  District  Court for the  District  of Delaware
relating  to the Merger  Agreement  and the  Mentor  Tender  Offer (the  "Mentor
Proposal"); and

         WHEREAS,  the Board of Directors of the Company has determined that the
Mentor  Proposal  constitutes  a Superior  Proposal  and the Company  desires to
terminate the Merger Agreement under Section 8.1(g) of the Merger Agreement upon
the terms and  conditions  of this  Agreement  and Parent  agrees to accept such
termination upon the terms and conditions of this Agreement.

         NOW,   THEREFORE,   in   consideration   of  the   premises,   and  the
representations, warranties, covenants, and agreements set forth herein, and for
other good and valuable consideration,  the receipt and sufficiency of which are
hereby acknowledged, the Parties agree as follows:

1. Termination of Merger Agreement.  The Parties agree that this Agreement shall
constitute  notice of termination  under Section 8.1(g) of the Merger Agreement.
Upon the  execution  and delivery of this  Agreement,  the Company  shall pay to
Parent the sum of five million five hundred  thousand  dollars  ($5,500,000)  by
irrevocable  wire  transfer  of  immediately  available  funds  to  the  account
identified on Schedule A. Effective and contingent upon such payment, the Merger
Agreement  shall be terminated  and the effects of  termination  shall be as set
forth in Section 8.2 (other than Section 8.2(b)) of the Merger Agreement.

2. Termination of Voting Agreements.  The Parties agree and acknowledge that the
Voting  Agreements shall terminate by their terms upon termination of the Merger
Agreement.

3. Releases.

(a) By Parent  and  Merger  Sub.  Subject  (as a  condition  subsequent)  to the
dismissal  with  prejudice  of the Deal Related  Litigation,  each of Parent and
Merger Sub, and each of their respective  successors and assigns,  shall forever
release and  discharge  the Company and each of its  respective  successors  and
assigns  (together with any present and former  officers,  directors,  and other
agents, representatives and advisors including any investment bankers, attorneys
or  accountants)  (the "Company  Releasees")  from any and all claims,  demands,
liens,  actions,  suits, causes of action,  obligations,  controversies,  debts,
costs, attorneys' fees, expenses, damages, judgments, orders, and liabilities of
whatever kind or nature at law, in equity,  or  otherwise,  whether now known or
unknown,  suspected  or  unsuspected,   liquidated  or  unliquidated,  fixed  or
contingent  and  whether or not  concealed  or hidden  (collectively,  "Claims")
relating  to or  arising  out  of  (i)  any  action  or  failure  to  act or any
misstatement  or omission,  in each case prior to the  execution and delivery of
this  Agreement  by the  Parties,  in actual or alleged  violation of the Merger
Agreement or the Voting Agreements or in actual or alleged breach of any duty or
obligation  in  connection  therewith  or (ii)  the  termination  of the  Merger
Agreement;  provided,  however,  that nothing  herein shall prevent or limit the
enforcement of rights and  obligations  (x) under the Merger  Agreement which by
the  terms  of the  Merger  Agreement  survive  the  termination  of the  Merger
Agreement or (y) under this Agreement;  and provided further that nothing herein
shall be  construed to release any of the Company  Releasees  from any Claim for
breach of any provision of the  Confidentiality  Agreement  which is intended to
survive  following an  acquisition of the Company by a third party or any of the
provisions  of the Merger  Agreement  (other than Section  8.2(b))  which by the
terms of Section 8.2 of the Merger Agreement  survive  termination of the Merger
Agreement.

(b) By the  Company.  The Company,  and each of its  respective  successors  and
assigns,  hereby forever releases and discharges  Parent and Merger Sub and each
of their respective successors and assigns (together with any present and former
officers,  directors,  and other agents,  representatives and advisors including
any investment bankers,  attorneys or accountants) (the "Parent Releasees") from
any Claims relating to or arising out of (i) any action or failure to act or any
misstatement  or omission,  in each case prior to the  execution and delivery of
this  Agreement  by the  Parties,  in actual or alleged  violation of the Merger
Agreement or the Voting Agreements or in actual or alleged breach of any duty or
obligation  in  connection  therewith  or (ii)  the  termination  of the  Merger
Agreement  or  the  payment  of the  termination  fee in  accordance  with  this
Agreement  and  Sections  8.1(g)  and  8.3 of the  Merger  Agreement;  provided,
however,  that nothing  herein shall prevent or limit the  enforcement of rights
and obligations (x) under the Merger  Agreement which by the terms of the Merger
Agreement  survive the  termination  of the Merger  Agreement  or (y) under this
Agreement;  and  provided  further  that  nothing  herein  shall be construed to
release any of the Parent  Releasees  from any Claim for breach of any provision
of the  Confidentiality  Agreement  which is  intended to survive  following  an
acquisition  of the  Company by a third  party or any of the  provisions  of the
Merger  Agreement  (other than Section 8.2(b)) which by the terms of Section 8.2
of the Merger Agreement survive termination of the Merger Agreement.

(c) Waiver of Other  Claims.  Each of the Parties  acknowledges  that there is a
possibility  that  subsequent  to the  execution  of this  Agreement,  they will
discover  facts or incur or suffer claims which were unknown or  unsuspected  at
the time this  Agreement was  executed,  and which if known by them at that time
may have materially  affected their decision to execute this Agreement.  Each of
the Parties  acknowledges  and agrees that by reason of this Agreement,  and the
release  contained in the  preceding  paragraphs,  they are assuming any risk of
such unknown facts and such unknown and unsuspected  claims. Each of the Parties
have been advised of the existence of Section 1542 of the California Civil Code,
which provides:

                  A GENERAL RELEASE DOES NOT EXTEND TO CLAIMS WHICH THE CREDITOR
                  DOES NOT KNOW OR  SUSPECT TO EXIST IN HIS FAVOR AT THE TIME OF
                  EXECUTING  THE  RELEASE,  WHICH  IF  KNOWN  BY HIM  MUST  HAVE
                  MATERIALLY AFFECTED HIS SETTLEMENT WITH THE DEBTOR.

Notwithstanding such provisions,  the releases contained in this Agreement shall
constitute  a full  release in  accordance  with its terms.  Each of the Parties
knowingly and  voluntarily  WAIVE the provisions of Section 1542, as well as any
other statute,  law, or rule of similar  effect,  and acknowledge and agree that
this waiver is an essential and material term of this release and the settlement
which leads to it, and without  such waiver the  settlement  would not have been
accepted.  This waiver includes, but is not limited to, a waiver of the right to
a claim of fraudulent inducement to enter into this Agreement as to such unknown
facts and such unknown and unsuspected claims,  except that it shall not include
misrepresentations  as to the  representations  and warranties  contained within
this Agreement. Each of the Parties hereby represent that they have been advised
by  their  legal  counsel,   and  that  they   understand  and  acknowledge  the
significance  and  consequence  of this release and of this  specific  waiver of
Section 1542 and other such laws of other jurisdictions.

4. Cooperation.  The Parties shall cooperate with each other to promptly prepare
and  file  all   necessary   documentation   to   withdraw   the   joint   proxy
statement/prospectus  filed by the Parties with the SEC in  connection  with the
Merger Agreement.

5.  Representations  of the Parent and Merger Sub.  Parent and Merger Sub,  each
represent that: (a) it is duly organized,  validly existing and in good standing
under  the laws of the State of  Delaware;  (b) it has all  requisite  corporate
power  and  authority  to enter  into  this  Agreement  and to take the  actions
contemplated  hereby;  (c) its execution and delivery of this  Agreement and the
actions contemplated hereby have been duly authorized by all necessary corporate
action;  and (d) this  Agreement  has  been  duly  executed  and  delivered  and
constitutes a valid and binding agreement,  enforceable against it in accordance
with its terms.


6.  Representations of the Company. The Company hereby represents that (a) it is
duly  organized,  validly  existing and in good  standing  under the laws of the
State of Delaware;  (b) it has all  requisite  corporate  power and authority to
enter into this Agreement and to take the actions  contemplated  hereby; (c) its
execution  and delivery of this  Agreement and the actions  contemplated  hereby
have been duly authorized by all necessary  corporate action; (d) this Agreement
has been duly  executed  and  delivered  and  constitutes  a valid  and  binding
agreement,  enforceable  against  it in  accordance  with  its  terms;  and  (e)
execution and delivery of this  Agreement and  compliance  with the terms hereof
(including  payment of the amount set forth in Section 1 hereof) do not and will
not breach the terms of any agreement to which the Company is a party.

7.  Amendment.  This  Agreement  may not be amended  except by  execution  of an
instrument in writing signed on behalf of each of the Parties.

8. Counterparts. This Agreement may be executed in one or more counterparts, all
of which  shall  be  considered  one and the same  agreement  and  shall  become
effective when one or more  counterparts have been signed by each of the Parties
and delivered to the other parties,  it being  understood  that all parties need
not sign the same counterpart.

9.  Entire  Agreement;  Assignment;  Parties in  Interest.  This  Agreement  (i)
constitutes  the entire  agreement among the Parties with respect to the subject
matter hereof and  supersedes  all prior  agreements  and  understandings,  both
written and oral,  among the Parties with respect to the subject  matter hereof;
(ii)  shall  not be  assigned  by any  Party,  whether  by  operation  of law or
otherwise;  and  (iii) is not  intended  to,  and  shall  not be  construed  as,
conferring upon any person other than the Parties any rights or remedies.

10.  Severability.  In the event that any  provision of this  Agreement,  or the
application thereof, becomes or is declared by a court of competent jurisdiction
to be illegal,  void or  unenforceable,  the  remainder of this  Agreement  will
continue in full force and effect and the application of such provision to other
persons or  circumstances  will be  interpreted  so as  reasonably to effect the
intent  of the  Parties.  The  Parties  further  agree to  replace  such void or
unenforceable provision of this Agreement with a valid and enforceable provision
that will achieve,  to the extent  possible,  the  economic,  business and other
purposes of such void or unenforceable provision.

11.  Governing  Law.  This  Agreement  shall be  governed  by and  construed  in
accordance  with the internal laws of the State of Delaware,  without  regard to
the laws that might otherwise govern under applicable principles of conflicts of
law. Each of the Parties irrevocably consents to the exclusive  jurisdiction and
venue of any court  located  within  the  County  of New  Castle in the State of
Delaware,  in  connection  with any matter  based  upon or  arising  out of this
Agreement or the matters contemplated herein,  agrees that process may be served
upon them in any manner authorized by the laws of the State of Delaware for such
persons and waives and covenants not to assert or plead any objection which they
might otherwise have to such jurisdiction and such process.





           SIGNATURE PAGE TO TERMINATION AGREEMENT AND MUTUAL RELEASE


                  IN WITNESS  WHEREOF,  the Company,  Parent and Merger Sub have
caused  this  Termination  Agreement  and  Mutual  Release  to be  executed  and
delivered by their respective officers thereunto duly authorized,  all as of the
date first written above.



                     SYNOPSYS, INC.



                     By:           /s/ Steven K. Shevick
                          Name:    Steven K. Shevick
                          Title:   Vice President, Legal and Investor Relations



                     IKOS SYSTEMS, INC.



                     By:           /s/ Ramon Nunez
                          Name:    Ramon Nunez
                          Title:   President and Chief Executive Officer



                   OAK MERGER CORPORATION



                     By:           /s/ Steven K. Shevick
                          Name:    Steven K. Shevick
                          Title:   Vice President and Secretary