<PAGE>   1
        As filed with the Securities and Exchange Commission on October 19, 2000
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      Under
                           THE SECURITIES ACT OF 1933

                                   HI/FN, INC.
               (Exact name of issuer as specified in its charter)

<TABLE>
<S>                                            <C>
        DELAWARE                                           33-0732700
(State of Incorporation)                       (IRS Employer Identification No.)
</TABLE>

                              750 University Avenue
                           Los Gatos, California 95302
                    (Address of principal executive offices)

                     APPTITUDE, INC. 1995 STOCK OPTION PLAN
                            (Full title of the plans)

                                  Chris Kenber
                             Chief Executive Officer
                              750 University Avenue
                           Los Gatos, California 95032
                     (Name and address of agent for service)

                                 (408) 399-3500
          (Telephone number, including area code, of agent for service)

                                    Copy to:

                             Steven E. Bochner, Esq.
                        WILSON SONSINI GOODRICH & ROSATI
                               650 Page Mill Road
                        Palo Alto, California 94304-1050

                         CALCULATION OF REGISTRATION FEE
<TABLE>
<CAPTION>
=======================================================================================
                                               AMOUNT TO     PROPOSED        AMOUNT OF
         TITLE OF SECURITIES                      BE       OFFERING PRICE  REGISTRATION
          TO BE REGISTERED                    REGISTERED    PER SHARE(1)       FEE
--------------------------------------------  ----------   --------------  ------------
<S>                                           <C>          <C>             <C>
Common Stock, par value $0.001 per share
--Outstanding under 1995 Stock Option Plan       690,000     $25.22         $4,600.00
</TABLE>

(1) With respect to the outstanding options to purchase Common Stock under the
1995 Stock Option Plan the computation of the proposed offering price per share
is based upon the weighted average exercise price per share of approximately
$25.22 as to 690,000 outstanding but unexercised options to purchase Common
Stock under the 1995 Stock Option Plan.



<PAGE>   2

                                   HI/FN, INC.

                       REGISTRATION STATEMENT ON FORM S-8

                                     PART II

                 INFORMATION REQUIRED IN REGISTRATION STATEMENT


ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE

         The Company hereby incorporates by reference in this Registration
Statement the contents of the Company's earlier Registration Statement on Form
S-8 (File #333-77331). In addition, there are hereby incorporated by reference
into this Registration Statement the following documents and information
heretofore filed by the Registrant with the Securities and Exchange Commission
(the "Commission"):

         o     hi/fn's Registration Statement on Form 10 (File No. 0-24765)
               filed December 8, 1998.

         o     hi/fn's annual report on Form 10-K filed on December 30, 1999.

         o     hi/fn's quarterly reports on Form 10-Q filed on February 14,
               2000, May 15, 2000 and August 8, 2000.

         All documents filed by the Company pursuant to Sections 13(a), 13(c),
14 and 15(d) of the 1934 Act on or after the date of this Registration Statement
and prior to the filing of a post-effective amendment which indicates that all
securities offered have been sold or which deregisters all securities then
remaining unsold shall be deemed to be incorporated by reference in this
Registration Statement and to be part hereof from the date of filing of such
documents.

ITEM 4.  DESCRIPTION OF SECURITIES.

         Inapplicable.

ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.

         Inapplicable.

ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.


         The Company's Certificate of Incorporation and Bylaws provide for the
indemnification of present and former directors, officers, employees and agents
of the Company and persons serving as directors, employees or agents of another
corporation or entity at the request of the Company (each, an "Indemnified
Party") to the fullest extent permitted by the Delaware General Corporation Law
("DGCL"). Indemnified Parties are specifically indemnified in the Company Bylaws
(the "Indemnification Provisions") for expenses, including attorneys' fees,
court costs, witness fees, judgments, fines and amounts paid in settlement
actually and reasonably incurred by an Indemnified Party in connection with a
threatened, pending or completed action, suit or proceeding (whether civil,
criminal, administrative or investigative) by reason of the fact that he is or
was a director or officer of the Company or is or was serving as a director,
officer, employee or agent of another corporation or entity at the request of
the Company. Such Indemnified Party must have acted in good faith and in a
manner he reasonably believed to be in or not opposed to the best interests of
the subject corporation and, with respect to any criminal action or proceeding,
must have had no reasonable cause to believe his conduct was unlawful.



<PAGE>   3

         The Indemnification Provisions and provisions for advancing expenses in
the Company Bylaws are expressly not exclusive of any other rights of
indemnification or advancement of expenses pursuant to any agreement, vote or
the stockholders or disinterested directors or pursuant to judicial direction.
The Company is authorized to purchase insurance on behalf of an Indemnified
Party for liabilities incurred, whether or not the Company would have the power
or obligation to indemnify him pursuant to the Company Certificate, the Company
Bylaws or the DGCL.

         In addition, the Company has entered, or will enter, into
indemnification agreements with each of its directors and executive officers
pursuant to which such persons are indemnified for costs and expenses actually
and reasonably incurred by such persons in connection with a threatened, pending
or completed claim arising out of service as a director, officer, employee,
trustee and/or agent of the Company or another entity at the request of the
Company.

ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.

         Inapplicable.

ITEM 8.  EXHIBITS.

<TABLE>
<CAPTION>
    EXHIBIT
    NUMBER                                 DESCRIPTION
    -------    -------------------------------------------------------------------------------
<S>            <C>
     4.1       Apptitude, Inc. 1995 Stock Option Plan
     5.1       Opinion of Wilson Sonsini Goodrich & Rosati, Professional Corporation, as to
               legality of securities being offered
    23.1       Consent of PricewaterhouseCoopers LLP, Independent Accountants
    23.2       Consent of Wilson Sonsini Goodrich & Rosati, Professional Corporation (included
               in Exhibit 5.1)
    24.1       Powers of Attorney (see page 5)
  ------------
</TABLE>

ITEM 9.  UNDERTAKINGS

         (a)   The undersigned Company hereby undertakes:

               (1) To file, during any period in which offers or sales are being
made, a post-effective amendment to this registration statement to include any
material information with respect to the plan of distribution not previously
disclosed in the registration statement or any material change to such
information in the registration statement.

               (2) That, for the purpose of determining any liability under the
1933 Act, each such post-effective amendment shall be deemed to be a new
registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

               (3) To remove from registration by means of a post-effective
amendment any of the securities being registered which remain unsold at the
termination of the offering.

         (b)   The undersigned Company hereby undertakes that, for purposes of
determining any liability under the 1933 Act, each filing of the Company's
annual report pursuant to Section 13(a) or Section 15(d) of the 1934 Act (and,
where applicable, each filing of an employee benefit plan's annual report
pursuant to Section 15(d) of the 1934 Act) that is incorporated by reference in
the registration statement shall be deemed to be a new registration statement
relating to the securities offered therein, and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.



                                       -2-
<PAGE>   4

         (c) Insofar as indemnification for liabilities arising under the 1933
Act may be permitted to directors, officers and controlling persons of the
Company pursuant to the foregoing provisions, or otherwise, the Company has been
advised that in the opinion of the Securities and Exchange Commission such
indemnification is against public policy as expressed in the Act and is,
therefore, unenforceable. In the event that a claim for indemnification against
such liabilities (other than the payment of the Company of expenses incurred or
paid by a director, officer or controlling person of the Company in the
successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the Company will, unless in the opinion of its counsel the matter
has been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the 1933 Act and will be governed by the final
adjudication of such issue.



                                       -3-
<PAGE>   5

                                   SIGNATURES



         Pursuant to the requirements of the 1933 Act, the Company, hi/fn, inc.,
a corporation organized and existing under the laws of the State of Delaware,
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Los Gatos, State of California, on this 19th day of
October, 2000.



                                        hi/fn, inc.




                                        By: /s/ Chris G. Kenber
                                           -------------------------------------
                                           Chris G. Kenber
                                           President, Chief Executive Officer &
                                           Director



                                       -4-
<PAGE>   6

                                POWER OF ATTORNEY



         KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature
appears below constitutes and appoints Chris Kenber and William R. Walker,
jointly and severally, his attorneys-in-fact, each with the power of
substitution, for him in any and all capacities, to sign any amendments to this
Registration Statement on Form S-8, and to file the same, with exhibits thereto
and other documents in connection therewith, with the Securities and Exchange
Commission, hereby ratifying and confirming all that each of said
attorneys-in-fact, or his substitute or substitutes, may do or cause to be done
by virtue hereof.

         Pursuant to the requirements of the 1933 Act, this Registration
Statement has been signed by the following persons in the capacities and on the
dates indicated.

<TABLE>
<CAPTION>
               SIGNATURE                                TITLE                         DATE
------------------------------------    ------------------------------------   -----------------
<S>                                     <C>                                    <C>
/s/ Chris G. Kenber
-----------------------------------      President, Chief Executive Officer
Chris G. Kenber                          and  Director                          October 19, 2000

/s/ William R. Walker
-----------------------------------      Vice President, Finance, Chief
William R. Walker                        Financial Officer and Secretary        October 19, 2000


/s/ Douglas L. Whiting
-----------------------------------      Director                               October 19, 2000
Douglas L. Whiting

/s/ Robert W. Johnson
-----------------------------------      Director                               October 19, 2000
Robert W. Johnson

/s/ Raymond J. Farnham
-----------------------------------       Director                              October 19, 2000
Raymond J. Farnham


/s /Taher Elgamal
-----------------------------------      Director                               October 19, 2000
Taher Elgamal

</TABLE>



                                       -5-
<PAGE>   7

                                INDEX TO EXHIBITS

<TABLE>
<CAPTION>

  EXHIBIT
  NUMBER                                 DESCRIPTION
-----------   ------------------------------------------------------------------
<S>           <C>
4.1           Apptitude, Inc. 1995 Stock Option Plan
5.1           Opinion of Counsel as to legality of securities being registered
23.1          Consent of Independent Accountants
23.2          Consent of Counsel (contained in Exhibit 5.1)
24.1          Power of Attorney (see Page 5)
</TABLE>



                                       -6-
[{"type": "S-8", "sequence": "1", "filename": "f66366s-8.txt", "description": "FORM S-8", "secsgml_size_bytes": 14115}]
{"company-data": {"conformed-name": "HI/FN INC", "cik": "0001065246", "assigned-sic": "3674", "irs-number": "330732700", "state-of-incorporation": "DE", "fiscal-year-end": "0930"}, "filing-values": {"form-type": "S-8", "act": "33", "file-number": "333-48232", "film-number": "742699"}, "business-address": {"street1": "750 UNIVERSITY AVENUE", "street2": "STE 230", "city": "LOS GATOS", "state": "CA", "zip": "95032", "phone": "4093993500"}, "mail-address": {"street1": "750 UNIVERSITY AVENUE", "street2": "STE 230", "city": "LOS GATOS", "state": "CA", "zip": "95032"}}
1
        As filed with the Securities and Exchange Commission on October 19, 2000
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      Under
                           THE SECURITIES ACT OF 1933

                                   HI/FN, INC.
               (Exact name of issuer as specified in its charter)
DELAWARE                                           33-0732700
(State of Incorporation)                       (IRS Employer Identification No.)
750 University Avenue
                           Los Gatos, California 95302
                    (Address of principal executive offices)

                     APPTITUDE, INC. 1995 STOCK OPTION PLAN
                            (Full title of the plans)

                                  Chris Kenber
                             Chief Executive Officer
                              750 University Avenue
                           Los Gatos, California 95032
                     (Name and address of agent for service)

                                 (408) 399-3500
          (Telephone number, including area code, of agent for service)

                                    Copy to:

                             Steven E. Bochner, Esq.
                        WILSON SONSINI GOODRICH & ROSATI
                               650 Page Mill Road
                        Palo Alto, California 94304-1050

                         CALCULATION OF REGISTRATION FEE
=======================================================================================
                                               AMOUNT TO     PROPOSED        AMOUNT OF
         TITLE OF SECURITIES                      BE       OFFERING PRICE  REGISTRATION
          TO BE REGISTERED                    REGISTERED    PER SHARE(1)       FEE
--------------------------------------------  ----------   --------------  ------------
Common Stock, par value $0.001 per share
--Outstanding under 1995 Stock Option Plan       690,000     $25.22         $4,600.00
(1) With respect to the outstanding options to purchase Common Stock under the
1995 Stock Option Plan the computation of the proposed offering price per share
is based upon the weighted average exercise price per share of approximately
$25.22 as to 690,000 outstanding but unexercised options to purchase Common
Stock under the 1995 Stock Option Plan.
2

                                   HI/FN, INC.

                       REGISTRATION STATEMENT ON FORM S-8

                                     PART II

                 INFORMATION REQUIRED IN REGISTRATION STATEMENT

ITEM 3.  INCORPORATION OF DOCUMENTS BY REFERENCE

         The Company hereby incorporates by reference in this Registration
Statement the contents of the Company's earlier Registration Statement on Form
S-8 (File #333-77331). In addition, there are hereby incorporated by reference
into this Registration Statement the following documents and information
heretofore filed by the Registrant with the Securities and Exchange Commission
(the "Commission"):

         o     hi/fn's Registration Statement on Form 10 (File No. 0-24765)
               filed December 8, 1998.

         o     hi/fn's annual report on Form 10-K filed on December 30, 1999.

         o     hi/fn's quarterly reports on Form 10-Q filed on February 14,
               2000, May 15, 2000 and August 8, 2000.

         All documents filed by the Company pursuant to Sections 13(a), 13(c),
14 and 15(d) of the 1934 Act on or after the date of this Registration Statement
and prior to the filing of a post-effective amendment which indicates that all
securities offered have been sold or which deregisters all securities then
remaining unsold shall be deemed to be incorporated by reference in this
Registration Statement and to be part hereof from the date of filing of such
documents.

ITEM 4.  DESCRIPTION OF SECURITIES.

         Inapplicable.

ITEM 5.  INTERESTS OF NAMED EXPERTS AND COUNSEL.

         Inapplicable.

ITEM 6.  INDEMNIFICATION OF DIRECTORS AND OFFICERS.

         The Company's Certificate of Incorporation and Bylaws provide for the
indemnification of present and former directors, officers, employees and agents
of the Company and persons serving as directors, employees or agents of another
corporation or entity at the request of the Company (each, an "Indemnified
Party") to the fullest extent permitted by the Delaware General Corporation Law
("DGCL"). Indemnified Parties are specifically indemnified in the Company Bylaws
(the "Indemnification Provisions") for expenses, including attorneys' fees,
court costs, witness fees, judgments, fines and amounts paid in settlement
actually and reasonably incurred by an Indemnified Party in connection with a
threatened, pending or completed action, suit or proceeding (whether civil,
criminal, administrative or investigative) by reason of the fact that he is or
was a director or officer of the Company or is or was serving as a director,
officer, employee or agent of another corporation or entity at the request of
the Company. Such Indemnified Party must have acted in good faith and in a
manner he reasonably believed to be in or not opposed to the best interests of
the subject corporation and, with respect to any criminal action or proceeding,
must have had no reasonable cause to believe his conduct was unlawful.
3

         The Indemnification Provisions and provisions for advancing expenses in
the Company Bylaws are expressly not exclusive of any other rights of
indemnification or advancement of expenses pursuant to any agreement, vote or
the stockholders or disinterested directors or pursuant to judicial direction.
The Company is authorized to purchase insurance on behalf of an Indemnified
Party for liabilities incurred, whether or not the Company would have the power
or obligation to indemnify him pursuant to the Company Certificate, the Company
Bylaws or the DGCL.

         In addition, the Company has entered, or will enter, into
indemnification agreements with each of its directors and executive officers
pursuant to which such persons are indemnified for costs and expenses actually
and reasonably incurred by such persons in connection with a threatened, pending
or completed claim arising out of service as a director, officer, employee,
trustee and/or agent of the Company or another entity at the request of the
Company.

ITEM 7.  EXEMPTION FROM REGISTRATION CLAIMED.

         Inapplicable.

ITEM 8.  EXHIBITS.
EXHIBIT
    NUMBER                                 DESCRIPTION
    -------    -------------------------------------------------------------------------------
4.1       Apptitude, Inc. 1995 Stock Option Plan
     5.1       Opinion of Wilson Sonsini Goodrich & Rosati, Professional Corporation, as to
               legality of securities being offered
    23.1       Consent of PricewaterhouseCoopers LLP, Independent Accountants
    23.2       Consent of Wilson Sonsini Goodrich & Rosati, Professional Corporation (included
               in Exhibit 5.1)
    24.1       Powers of Attorney (see page 5)
  ------------
ITEM 9.  UNDERTAKINGS

         (a)   The undersigned Company hereby undertakes:

               (1) To file, during any period in which offers or sales are being
made, a post-effective amendment to this registration statement to include any
material information with respect to the plan of distribution not previously
disclosed in the registration statement or any material change to such
information in the registration statement.

               (2) That, for the purpose of determining any liability under the
1933 Act, each such post-effective amendment shall be deemed to be a new
registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

               (3) To remove from registration by means of a post-effective
amendment any of the securities being registered which remain unsold at the
termination of the offering.

         (b)   The undersigned Company hereby undertakes that, for purposes of
determining any liability under the 1933 Act, each filing of the Company's
annual report pursuant to Section 13(a) or Section 15(d) of the 1934 Act (and,
where applicable, each filing of an employee benefit plan's annual report
pursuant to Section 15(d) of the 1934 Act) that is incorporated by reference in
the registration statement shall be deemed to be a new registration statement
relating to the securities offered therein, and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.

                                       -2-
4

         (c) Insofar as indemnification for liabilities arising under the 1933
Act may be permitted to directors, officers and controlling persons of the
Company pursuant to the foregoing provisions, or otherwise, the Company has been
advised that in the opinion of the Securities and Exchange Commission such
indemnification is against public policy as expressed in the Act and is,
therefore, unenforceable. In the event that a claim for indemnification against
such liabilities (other than the payment of the Company of expenses incurred or
paid by a director, officer or controlling person of the Company in the
successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the Company will, unless in the opinion of its counsel the matter
has been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the 1933 Act and will be governed by the final
adjudication of such issue.

                                       -3-
5

                                   SIGNATURES

         Pursuant to the requirements of the 1933 Act, the Company, hi/fn, inc.,
a corporation organized and existing under the laws of the State of Delaware,
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Los Gatos, State of California, on this 19th day of
October, 2000.

                                        hi/fn, inc.

                                        By: /s/ Chris G. Kenber
                                           -------------------------------------
                                           Chris G. Kenber
                                           President, Chief Executive Officer &
                                           Director

                                       -4-
6

                                POWER OF ATTORNEY

         KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature
appears below constitutes and appoints Chris Kenber and William R. Walker,
jointly and severally, his attorneys-in-fact, each with the power of
substitution, for him in any and all capacities, to sign any amendments to this
Registration Statement on Form S-8, and to file the same, with exhibits thereto
and other documents in connection therewith, with the Securities and Exchange
Commission, hereby ratifying and confirming all that each of said
attorneys-in-fact, or his substitute or substitutes, may do or cause to be done
by virtue hereof.

         Pursuant to the requirements of the 1933 Act, this Registration
Statement has been signed by the following persons in the capacities and on the
dates indicated.
SIGNATURE                                TITLE                         DATE
------------------------------------    ------------------------------------   -----------------
/s/ Chris G. Kenber
-----------------------------------      President, Chief Executive Officer
Chris G. Kenber                          and  Director                          October 19, 2000

/s/ William R. Walker
-----------------------------------      Vice President, Finance, Chief
William R. Walker                        Financial Officer and Secretary        October 19, 2000

/s/ Douglas L. Whiting
-----------------------------------      Director                               October 19, 2000
Douglas L. Whiting

/s/ Robert W. Johnson
-----------------------------------      Director                               October 19, 2000
Robert W. Johnson

/s/ Raymond J. Farnham
-----------------------------------       Director                              October 19, 2000
Raymond J. Farnham

/s /Taher Elgamal
-----------------------------------      Director                               October 19, 2000
Taher Elgamal
-5-
7

                                INDEX TO EXHIBITS
EXHIBIT
  NUMBER                                 DESCRIPTION
-----------   ------------------------------------------------------------------
4.1           Apptitude, Inc. 1995 Stock Option Plan
5.1           Opinion of Counsel as to legality of securities being registered
23.1          Consent of Independent Accountants
23.2          Consent of Counsel (contained in Exhibit 5.1)
24.1          Power of Attorney (see Page 5)
-6-