AS FILED WITH THE SECURITIES AND EXCHANGE COMMISSION ON NOVEMBER 4, 1998
    
 
                                                      REGISTRATION NO. 333-64737
- --------------------------------------------------------------------------------
- --------------------------------------------------------------------------------
 
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
 
                            ------------------------
 
   
                                AMENDMENT NO. 1
                                       TO
                                    FORM S-3
    
 
            REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933
                            ------------------------
 

                                                             
                        IDACORP, INC.                                                  IDACORP TRUST I
                 (Exact name of registrant as                                          IDACORP TRUST II
                    specified in charter)                                             IDACORP TRUST III
                            IDAHO                                             (Exact name of each registrant as
                 (State or other jurisdiction                                 specified in its Trust Agreement)
              of incorporation or organization)                                            DELAWARE
                          82-0505802                                           (State or other jurisdiction of
             (I.R.S. Employer Identification No.)                     incorporation or organization of each registrant)
                                                                                    EACH TO BE APPLIED FOR
                    1221 WEST IDAHO STREET                                   (I.R.S. Employer Identification No.)
                   BOISE, IDAHO 83702-5627                                            C/O IDACORP, INC.
                         208-388-2200                                               1221 WEST IDAHO STREET
(Address, including zip code, and telephone number, including                      BOISE, IDAHO 83702-5627
   area code, of registrant's principal executive offices)                               208-388-2200
                                                                     (Address, including zip code, and telephone number,
                                                                   including area code, of registrant's principal executive
                                                                                           offices)

 
                            ------------------------
 

                                         
            JOSEPH W. MARSHALL                            J. LAMONT KEEN
        CHAIRMAN OF THE BOARD AND            VICE PRESIDENT, CHIEF FINANCIAL OFFICER
         CHIEF EXECUTIVE OFFICER                          AND TREASURER
              IDACORP, INC.                               IDACORP, INC.
          1221 WEST IDAHO STREET                      1221 WEST IDAHO STREET
         BOISE, IDAHO 83702-5627                     BOISE, IDAHO 83702-5627
               208-388-2200                                208-388-2200
         ROBERT W. STAHMAN, ESQ.                    ELIZABETH W. POWERS, ESQ.
     VICE PRESIDENT, GENERAL COUNSEL          LEBOEUF, LAMB, GREENE & MACRAE, L.L.P.
              AND SECRETARY                            125 WEST 55TH STREET
              IDACORP, INC.                          NEW YORK, NEW YORK 10019
          1221 WEST IDAHO STREET                           212-424-8000
         BOISE, IDAHO 83702-5627
               208-388-2200

 
   
 (Names, addresses, including zip codes, and telephone numbers, including area
                         codes, of agents for service)
    
 
                         ------------------------------
 
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- --------------------------------------------------------------------------------

   
                  SUBJECT TO COMPLETION DATED NOVEMBER 4, 1998
    
INFORMATION CONTAINED HEREIN IS SUBJECT TO COMPLETION OR AMENDMENT. A
REGISTRATION STATEMENT RELATING TO THESE SECURITIES HAS BEEN FILED WITH THE
SECURITIES AND EXCHANGE COMMISSION. THESE SECURITIES MAY NOT BE SOLD NOR MAY
OFFERS TO BUY BE ACCEPTED PRIOR TO THE TIME THE REGISTRATION STATEMENT BECOMES
EFFECTIVE. THIS PROSPECTUS SHALL NOT CONSTITUTE AN OFFER TO SELL OR THE
SOLICITATION OF AN OFFER TO BUY NOR SHALL THERE BE ANY SALE OF THESE SECURITIES
IN ANY JURISDICTION IN WHICH SUCH OFFER, SOLICITATION OR SALE WOULD BE UNLAWFUL
PRIOR TO REGISTRATION OR QUALIFICATION UNDER THE SECURITIES LAWS OF ANY SUCH
JURISDICTION.

PROSPECTUS
 
                                  $300,000,000
 
   
                                 IDACORP, INC.
    
 
              DEBT SECURITIES, PREFERRED STOCK, DEPOSITORY SHARES
                                AND COMMON STOCK
                               ------------------
 
                                IDACORP TRUST I
 
                                IDACORP TRUST II
 
                               IDACORP TRUST III
 
   
    PREFERRED SECURITIES FULLY AND UNCONDITIONALLY GUARANTEED, TO THE EXTENT
                              DESCRIBED HEREIN, BY
                                 IDACORP, INC.
    
 
   
    IDACORP, Inc., an Idaho corporation ("IDACORP" or the "Company"), may offer
and sell from time to time, together or separately, (i) its unsecured debt
securities (the "Debt Securities"), which may be senior (the "Senior Debt
Securities") or subordinated in priority of payment (the "Subordinated Debt
Securities"), (ii) shares of its preferred stock, without par value (the
"Preferred Stock"), which may be represented by depository shares as described
herein (the "Depository Shares"), and (iii) shares of its common stock, without
par value, including the Rights (as defined herein) attached thereto (the
"Common Stock"). The Debt Securities, the Preferred Stock and the Common Stock,
together with the Preferred Securities and the related Guarantees (each as
defined below), are collectively referred to herein as the "Securities." The
Securities may be offered in one or more separate classes or series, in amounts,
at prices and on terms to be determined at the time of the offering thereof and
to be set forth in a supplement or supplements to this Prospectus (each, a
"Prospectus Supplement").
    
 
    IDACORP Trust I, IDACORP Trust II and IDACORP Trust III, each a statutory
business trust created under the laws of the State of Delaware (each, an
"IDACORP Trust," and collectively, the "IDACORP Trusts"), may severally offer
preferred securities (the "Preferred Securities") representing undivided
beneficial ownership interests in the assets of such IDACORP Trust. The Company
will be the owner of the common securities (the "Common Securities" and,
together with the Preferred Securities, the "Trust Securities") of each IDACORP
Trust. The payment of periodic cash distributions (the "Distributions") with
respect to the Preferred Securities of each IDACORP Trust and payments on
liquidation and on redemption with respect to such Preferred Securities in each
case out of funds held by such IDACORP Trust will each be guaranteed by the
Company as and to the extent described herein (each, a "Guarantee"). See
"Description of Guarantees." The Company's obligations under each Guarantee are
an unsecured obligation of the Company and will rank subordinate and junior in
right of payment to all Senior Indebtedness and Subordinated Indebtedness (each
as defined herein) of the Company. Except as otherwise provided in the
applicable Prospectus Supplement, (i) concurrently with the issuance by an
IDACORP Trust of its Preferred Securities, such IDACORP Trust will invest the
proceeds thereof and any contributions made in respect of the Common Securities
in a corresponding series of the Company's Subordinated Debt Securities (the
"Corresponding Subordinated Debt Securities") with terms directly corresponding
to the terms of that IDACORP Trust's Preferred Securities, (ii) the
Corresponding Subordinated Debt Securities will be the sole assets of each
IDACORP Trust and (iii) payments under the Corresponding Subordinated Debt
Securities will be the only revenue of each IDACORP Trust. Unless otherwise
specified in an applicable Prospectus Supplement, the Company may redeem the
Corresponding Subordinated Debt Securities (and cause the redemption of Trust
Securities) or may dissolve each IDACORP Trust and, after satisfaction of
creditors of such IDACORP Trusts as provided by applicable law, cause the
Corresponding Subordinated Debt Securities to be distributed to the holders of
Preferred Securities in liquidation of their interests in the applicable IDACORP
Trust. See "Description of Preferred Securities-- Liquidation Distribution Upon
Dissolution."
                            ------------------------
 THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY THE SECURITIES AND
     EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION NOR HAS THE
     SECURITIES AND EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION
         PASSED UPON THE ACCURACY OR ADEQUACY OF THIS PROSPECTUS. ANY
            REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.
                            ------------------------
 
       This Prospectus may not be used to consummate sales of Securities
                 unless accompanied by a Prospectus Supplement.
 
               The date of this Prospectus is            , 1998.

    The specific terms of the Securities in respect of which this Prospectus is
being delivered will be set forth in the accompanying Prospectus Supplement or
Supplements, together with the terms of the offering of any such Securities, the
initial price thereof and the net proceeds from the sale thereof. The Prospectus
Supplement will also set forth with respect to the particular Securities
offered, certain terms thereof, including, where applicable, (i) in the case of
Debt Securities, the title of the series being offered thereby, aggregate
principal amount of such series, authorized denominations and priority thereof,
the date or dates on which such Debt Securities will mature, the rate or rates
per annum at which such Debt Securities will bear interest, if any, or the
method of determination of such rate or rates, the dates on which such interest,
if any, will be payable, and record dates, if any, for such payment dates, the
deferral of payment of any interest, any redemption or sinking fund provisions,
the place or places for payment of the principal of and any premium and interest
on such Debt Securities and any additional or other rights, preferences,
privileges, limitations and restrictions relating to such Debt Securities, (ii)
in the case of Preferred Stock, the number of shares constituting such series
and the designation thereof; the rate or rates of dividend, if any, or any
formula or other method or other means by which such rate or rates are to be
determined at any time or from time to time, the date or dates on which
dividends may be payable, whether such dividends shall be cumulative,
noncumulative or partially cumulative and, if cumulative or partially
cumulative, the date from which dividends shall accumulate; whether shares may
be redeemed or converted (a) at the option of the Company, the shareholder or
another person or upon the occurrence of a designated event; (b) for cash,
indebtedness, securities or other property; (c) in a designated amount or in an
amount determined in accordance with a designated formula or by reference to
extrinsic data or events; the preference, if any, of shares of such series over
any other class of shares with respect to distributions, including dividends and
distributions upon any voluntary or involuntary dissolution, liquidation or
winding up of the Company; whether the shares shall have any voting powers, in
addition to the voting powers provided by law, and the terms of any such voting
powers; and any other relative rights, preferences and limitations of that
series, (iii) in the case of Common Stock, the aggregate number of shares
offered, the initial offering price and market price and dividend information
and (iv) in the case of Preferred Securities of an IDACORP Trust, the specific
designation, number of securities, liquidation amount per security, any listing
on a securities exchange, distribution rate (or method of calculation thereof),
dates on which distributions shall be payable and dates from which distributions
shall accrue, voting rights, if any, terms for any conversion or exchange into
other securities, any redemption or sinking fund provisions, any other rights,
preferences, privileges, limitations or restrictions relating to the Preferred
Securities and the terms upon which the proceeds of the sale of the Preferred
Securities shall be used to purchase a specific series of Corresponding
Subordinated Debt Securities of the Company. The Prospectus Supplement will also
contain information, where applicable, about certain United States Federal
income tax considerations relating to the Securities described in the Prospectus
Supplement. All or a portion of the Securities may be issued in permanent or
temporary global form (each a "Global Security").
 
    The aggregate initial offering price of all Securities shall not exceed
$300,000,000.
 
    The Securities may be sold through underwriters or dealers or may be sold by
the Company and/or each IDACORP Trust directly or through agents designated from
time to time. The names of any underwriters or agents involved in the sale of
the Securities in respect of which this Prospectus is being delivered and their
compensation will be set forth in the Prospectus Supplement.
 
                                       2

    NO DEALER, SALESMAN OR OTHER PERSON HAS BEEN AUTHORIZED TO GIVE ANY
INFORMATION OR TO MAKE ANY REPRESENTATION NOT CONTAINED IN THIS PROSPECTUS OR
THE ACCOMPANYING PROSPECTUS SUPPLEMENT AND, IF GIVEN OR MADE, SUCH INFORMATION
OR REPRESENTATION MUST NOT BE RELIED UPON AS HAVING BEEN AUTHORIZED BY THE
COMPANY, THE IDACORP TRUSTS OR ANY UNDERWRITER, DEALER OR AGENT. THIS PROSPECTUS
AND THE ACCOMPANYING PROSPECTUS SUPPLEMENT DO NOT CONSTITUTE AN OFFER TO SELL OR
A SOLICITATION OF AN OFFER TO BUY ANY OF THE SECURITIES OFFERED HEREBY IN ANY
JURISDICTION TO ANY PERSON TO WHOM IT IS UNLAWFUL TO MAKE SUCH OFFER IN SUCH
JURISDICTION. NEITHER THE DELIVERY OF THIS PROSPECTUS OR ANY PROSPECTUS
SUPPLEMENT NOR ANY SALE MADE HEREUNDER OR THEREUNDER SHALL, UNDER ANY
CIRCUMSTANCES, CREATE ANY IMPLICATION THAT THERE HAS BEEN NO CHANGE IN THE
AFFAIRS OF THE COMPANY SINCE THE DATE HEREOF.
                            ------------------------
 
                             AVAILABLE INFORMATION
 
    The Company is subject to the informational requirements of the Securities
Exchange Act of 1934, as amended (the "Exchange Act"), and in accordance
therewith files reports and other information with the Securities and Exchange
Commission (the "Commission"). The Company is a successor registrant to, and a
holding company owning all of the outstanding common shares of, Idaho Power
Company. Idaho Power Company ("Idaho Power") is also subject to the
informational requirements of the Exchange Act and in accordance therewith files
reports and other information with the Commission. The reports and other
information filed by the Company and Idaho Power can be inspected and copied at
the offices of the Commission at 450 Fifth Street, N.W., Washington, D.C. 20549;
500 West Madison Street, Chicago, Illinois 60661; and Seven World Trade Center,
New York, New York 10048. Copies of such material can be obtained from the
Public Reference Section of the Commission at 450 Fifth Street, N.W.,
Washington, D.C. 20549 at prescribed rates. In addition, the Commission
maintains a Website that contains reports and other information regarding
registrants that file electronically such as the Company. The address of the
Commission's Website is http://www.sec.gov. The Company's Common Stock is listed
on the New York Stock Exchange and the Pacific Exchange (the "Exchanges"), and
the aforementioned reports and other information concerning the Company may be
inspected at the offices of the New York Stock Exchange, 20 Broad Street, New
York, New York 10005 and the Pacific Exchange, 301 Pine Street, San Francisco,
California 94104.
 
    The Company and the IDACORP Trusts have filed with the Commission a
Registration Statement on Form S-3 (together with all amendments and exhibits
thereto, the "Registration Statement") under the Securities Act of 1933, as
amended (the "Securities Act") with respect to the securities offered hereby.
This Prospectus does not contain all the information set forth in the
Registration Statement, certain portions of which have been omitted as permitted
by the rules and regulations of the Commission. For further information with
respect to the Company and the securities offered hereby, reference is made to
the Registration Statement and the exhibits and the financial statements, notes
and schedules filed as a part thereof or incorporated by reference therein,
which may be inspected at the public reference facilities of the Commission at
the addresses set forth above. Statements made in this Prospectus concerning the
contents of any documents referred to herein are not necessarily complete and in
each instance are qualified in all respects by reference to the copy of such
document filed as an exhibit to the Registration Statement.
 
    No separate financial statements of the IDACORP Trusts have been included
herein. The Company and the IDACORP Trusts do not consider that such financial
statements would be material to holders of the Preferred Securities because (i)
all of the voting securities of the IDACORP Trusts will be owned, directly or
indirectly, by the Company, a reporting company under the Exchange Act, (ii)
each IDACORP Trust is a newly-formed special purpose entity, has no operating
history or independent operations and is not engaged in and does not propose to
engage in any activity other than holding as trust assets the Corresponding
Subordinated Debt Securities of the Company and issuing the Trust Securities and
(iii) the Company's obligations described herein and in any accompanying
Prospectus Supplement, through the applicable Guarantee (as defined herein), the
applicable Trust Agreement (as defined herein), the
 
                                       3

Subordinated Debt Securities, the Subordinated Indenture and any supplemental
indentures thereto, taken together, constitute a full, irrevocable and
unconditional guarantee by the Company of payments due on the Preferred
Securities. No single document standing alone or operating in conjunction with
fewer than all of the other documents constitutes such guarantee. It is only the
combined operation of these documents that has the effect of providing a full,
irrevocable and unconditional guarantee of the IDACORP Trust's obligations under
the Preferred Securities. See "The IDACORP Trusts," "Description of Preferred
Securities," "Description of the Debt Securities--Subordinated Debt
Securities--Subordination" and "Description of Guarantees."
 
                      DOCUMENTS INCORPORATED BY REFERENCE
 
    The following documents, which have been filed by Idaho Power Company and
IDACORP with the Securities and Exchange Commission, are incorporated by
reference herein and shall be deemed to be a part hereof:
 
    Idaho Power Company:
 
        1.  Annual Report on Form 10-K for the year ended December 31, 1997.
 
        2.  Quarterly Reports on Form 10-Q for the quarters ended March 31, 1998
    and June 30, 1998.
 
        3.  Current Report on Form 8-K, dated October 1, 1998.
 
    IDACORP:
 
        1.  Current Reports on Form 8-K, dated September 15, 1998 and October 1,
    1998.
 
        2.  Description of Common Stock contained in the Proxy Statement and
            Prospectus and Registration Statement on Form S-4 (File No.
            333-48031).
 
        3.  Description of the Preferred Share Purchase Rights contained in the
            Registration Statement on Form 8-A, dated September 15, 1998.
 
    All documents filed by the Company pursuant to Section 13(a), 13(c), 14 or
15(d) of the Exchange Act after the date hereof and prior to the termination of
the offering of the Securities offered hereby shall be deemed to be incorporated
by reference herein and to be a part hereof from the date of filing such
documents (such documents and the documents enumerated above being hereinafter
referred to as the "Incorporated Documents").
 
    Any statement contained herein or in a document incorporated or deemed to be
incorporated by reference in this Prospectus or in any Prospectus Supplement
shall be deemed to be modified or superseded for purposes of this Prospectus or
any Prospectus Supplement to the extent that a statement contained in this
Prospectus or in any Prospectus Supplement or in any other subsequently filed
document which also is or is deemed to be incorporated by reference in this
Prospectus or in any Prospectus Supplement modifies or supersedes such
statement. Any statement so modified or superseded shall not be deemed, except
as so modified or superseded, to constitute a part of this Prospectus or any
Prospectus Supplement.
 
    THE COMPANY WILL FURNISH WITHOUT CHARGE TO EACH PERSON, INCLUDING ANY
BENEFICIAL OWNER, TO WHOM THIS PROSPECTUS IS DELIVERED, UPON WRITTEN OR ORAL
REQUEST BY SUCH PERSON, A COPY OF ANY OR ALL OF THE INFORMATION THAT HAS BEEN
INCORPORATED BY REFERENCE HEREIN (NOT INCLUDING EXHIBITS THERETO UNLESS SUCH
EXHIBITS ARE SPECIFICALLY INCORPORATED BY REFERENCE THEREIN). REQUESTS SHOULD BE
ADDRESSED TO: SHAREOWNER SERVICES, IDACORP, 1221 WEST IDAHO STREET, BOISE, ID
83702-5627 OR MADE BY CALLING TOLL FREE 1-800-635-5406.
                            ------------------------
 
                                       4

                                  THE COMPANY
 
    IDACORP is a successor registrant to and a holding company owning all of the
outstanding common shares of Idaho Power Company. IDACORP was formed to effect
the organization into a holding company structure. Pursuant to the terms of the
Agreement and Plan of Exchange dated February 2, 1998, between Idaho Power and
IDACORP, on October 1, 1998 each share of Idaho Power Company Common Stock was
exchanged for one share of IDACORP Common Stock, and Idaho Power became a
subsidiary of IDACORP. As of the date of this Prospectus, IDACORP has no
separate operating history.
 
    Idaho Power is an electric public utility incorporated under the laws of the
state of Idaho in 1989 as successor to a Maine corporation organized in 1915.
Idaho Power is engaged in the generation, purchase, transmission, distribution
and sale of electric energy in an approximate 20,000-square-mile area in
southern Idaho, eastern Oregon and northern Nevada, with an estimated population
of 772,000. Idaho Power holds franchises in approximately 70 cities in Idaho and
10 cities in Oregon and holds certificates from the respective public utility
regulatory authorities to serve all or a portion of 28 counties in Idaho, three
counties in Oregon and one county in Nevada.
 
    Idaho Power operates 17 hydro power plants and shares ownership in three
coal-fired generating plants. Idaho Power relies heavily on hydroelectric power
for its generating needs and is one of the nation's few investor-owned utilities
with a predominantly hydro base. Idaho Power has participated in the development
of thermal generation in Wyoming, Oregon and Nevada using low-sulfur coal from
Wyoming and Utah.
 
    IDACORP also owns all of the outstanding securities of one of the former
non-utility subsidiaries of Idaho Power, Ida-West Energy Co. ("Ida-West").
Ida-West was formed in 1989 as an independent power producer and currently holds
investments in thirteen operating hydroelectric plants with a total generating
capacity of approximately 72 megawatts (MW). A subsidiary of Ida-West operates
and maintains ten of these plants. Ida-West owns a 50% interest in five
hydroelectric projects in Idaho with a total generating capacity of 33.4 MW.
 
    At December 31, 1997, Idaho Power had invested $20 million in Ida-West.
 
    The principal executive offices of the Company are located at 1221 West
Idaho Street, Boise, ID 83702-5627, and its telephone number is 208-388-2200.
 
             IDAHO POWER COMPANY RATIO OF EARNINGS TO FIXED CHARGES
              AND RATIO OF EARNINGS TO COMBINED FIXED CHARGES AND
                     PREFERRED STOCK DIVIDEND REQUIREMENTS


                                                                                            12 MONTHS ENDED
                                                                              --------------------------------------------
                                                                                                    DECEMBER 31,
                                                                               JUNE 30,    -------------------------------
IDAHO POWER COMPANY                                                              1998        1997       1996       1995
- ----------------------------------------------------------------------------  -----------  ---------  ---------  ---------
                                                                                                     
Ratio of Earnings to Fixed Charges..........................................        3.23        3.25       3.45       3.36
Supplemental Ratio of Earnings to Fixed Charges(1)..........................        3.14        3.16       3.34       3.26
Ratio of Earnings to Combined Fixed Charges and Preferred Stock Dividend
  Requirements..............................................................        2.83        2.88       2.85       2.76
Supplemental Ratio of Earnings to Combined Fixed Charges and Preferred Stock
  Dividend Requirements(1)..................................................        2.76        2.82       2.79       2.70
 

 
IDAHO POWER COMPANY                                                             1994       1993
- ----------------------------------------------------------------------------  ---------  ---------
                                                                                   
Ratio of Earnings to Fixed Charges..........................................       2.98       3.10
Supplemental Ratio of Earnings to Fixed Charges(1)..........................       2.89       3.01
Ratio of Earnings to Combined Fixed Charges and Preferred Stock Dividend
  Requirements..............................................................       2.49       2.70
Supplemental Ratio of Earnings to Combined Fixed Charges and Preferred Stock
  Dividend Requirements(1)..................................................       2.44       2.64

 
- ------------------------
 
(1) Includes fixed charges related to Idaho Power's guarantees of long-term
    bonds of the American Falls Reservoir District and Milner Dam Inc.
 
                                       5

                               THE IDACORP TRUSTS
 
    Each IDACORP Trust is a statutory business trust created under Delaware law
pursuant to (i) a trust agreement executed by the Company, as sponsor of such
IDACORP Trust (the "Sponsor"), and the Issuer Trustees (as defined herein) of
such IDACORP Trust and (ii) a certificate of trust filed with the Delaware
Secretary of State. Each trust agreement will be amended and restated in its
entirety (each, as so amended and restated, a "Trust Agreement") substantially
in the form filed as an exhibit to the Registration Statement of which this
Prospectus forms a part. Each Trust Agreement will be qualified as an indenture
under the Trust Indenture Act of 1939, as amended (the "Trust Indenture Act").
Each IDACORP Trust exists for the exclusive purposes of (i) issuing and selling
the Trust Securities representing undivided beneficial interests in the assets
of such IDACORP Trust, (ii) using the proceeds from the sale of such Trust
Securities to acquire a series of Corresponding Subordinated Debt Securities
issued by the Company and (iii) engaging in only those other activities
necessary, convenient or incidental thereto. Accordingly, the Corresponding
Subordinated Debentures will be the sole revenue source of each IDACORP Trust.
Each of the IDACORP Trusts is a separate legal entity, and the assets of one are
not available to satisfy the obligations of any of the others.
 
    All of the Common Securities of each IDACORP Trust will be owned by the
Company. The Common Securities of an IDACORP Trust will rank PARI PASSU, and
payments will be made thereon PRO RATA, with the Preferred Securities of such
IDACORP Trust, except that upon the occurrence and continuance of a Trust Event
of Default (as defined herein) resulting from an Event of Default with respect
to the Corresponding Subordinated Debt Securities, the rights of the Company as
holder of the Common Securities to payment in respect of Distributions and
payments upon liquidation, redemption or otherwise will be subordinated to the
rights of the holders of the Preferred Securities of such IDACORP Trust. See
"Description of Preferred Securities--Subordination of Common Securities." The
Company will acquire Common Securities in an aggregate liquidation amount equal
to not less than 3% of the total capital of each IDACORP Trust.
 
   
    Unless otherwise specified in the applicable Prospectus Supplement, each
IDACORP Trust has a term of approximately 50 years but may dissolve earlier as
provided in the applicable Trust Agreement. Each IDACORP Trust's business and
affairs will be conducted by its trustees, each appointed by the Company as
holder of the Common Securities. Unless otherwise specified in the applicable
Prospectus Supplement, the trustees for each IDACORP Trust will be Bankers Trust
Company ("Bankers Trust"), as the Property Trustee (the "Property Trustee"),
Bankers Trust Delaware, as the Delaware Trustee (the "Delaware Trustee"), and
two individual trustees (the "Administrative Trustees") who are employees or
officers of the Company (collectively, the "Issuer Trustees"). Bankers Trust, as
Property Trustee, will act as sole indenture trustee under each Trust Agreement
for purposes of compliance with the Trust Indenture Act. Unless otherwise
specified in the applicable Prospectus Supplement, Bankers Trust will act as
trustee under the Guarantee and the Subordinated Indenture (as defined herein)
until removed or replaced by the holder of the Common Securities of such IDACORP
Trust. See "Description of Guarantees" and "Description of the Debt
Securities--Subordinated Debt Securities--Subordination." Unless a Trust Event
of Default resulting from an Event of Default with respect to Corresponding
Subordinated Debt Securities for such IDACORP Trust has occurred and is
continuing, the Company, as the holder of the Common Securities of an IDACORP
Trust, may remove any of the Issuer Trustees. If such a Trust Event of Default
has occurred, the Company or the holders of a majority in liquidation amount of
the Preferred Securities will be entitled to appoint, remove or replace the
Property Trustee and/or the Delaware Trustee for such IDACORP Trust. In no event
will the holders of the Preferred Securities have the right to vote to appoint,
remove or replace the Administrative Trustees; such voting rights are vested
exclusively in the Company, as the holder of the Common Securities. The duties
and obligations of each Issuer Trustee are governed by the applicable Trust
Agreement. See "Description of Guarantees" and "Description of the Preferred
Securities."
    
 
    The principal executive office of each IDACORP Trust is c/o IDACORP, 1221
West Idaho Street, Boise, Idaho 83702 and its telephone number is 208-388-2200.
 
                                       6

                            APPLICATION OF PROCEEDS
 
    Unless otherwise specified in the Prospectus Supplement which accompanies
this Prospectus, the net proceeds from the sale of the Securities (other than
Trust Securities) will be added to the general funds of the Company to be
applied to fund investments in, or extensions of credit to, its subsidiaries; to
reduce other outstanding indebtedness; to fund acquisitions by the Company and
its subsidiaries of other companies; or for such other purposes as may be set
forth in the Prospectus Supplement. Pending such application, such net proceeds
may be temporarily invested in or applied to the reduction of short-term debt.
The Company expects from time to time to continue to incur short-term and
long-term debt and to effect other financings, the amounts of which cannot now
be determined. Each IDACORP Trust will use all proceeds received from the sale
of its Trust Securities to purchase the applicable Corresponding Subordinated
Debt Securities.
 
                       DESCRIPTION OF THE DEBT SECURITIES
 
    The following description sets forth certain general terms and provisions of
the Debt Securities to which any Prospectus Supplement may relate. The
particular terms of the Debt Securities offered by any Prospectus Supplement and
the extent, if any, to which such general provisions may apply to the Debt
Securities so offered will be described in the Prospectus Supplement relating to
such Debt Securities.
 
GENERAL
 
   
    The Debt Securities will constitute senior unsecured debt or subordinated
unsecured debt of the Company. The Debt Securities will be issued under a senior
indenture described below, for Senior Debt Securities (the "Senior Indenture")
and a subordinated indenture described below, for Subordinated Debt Securities
(the "Subordinated Indenture"), in each case between the Company and a banking
institution organized under the laws of the United States of America or of any
State thereof (each, an "Indenture Trustee") initially, Bankers Trust. The
Senior Debt Securities will rank PARI PASSU with all outstanding unsecured debt
of the Company that is not subordinated by its terms and will constitute part of
the Senior Indebtedness for purposes of the Subordinated Indenture. The Senior
Indenture and the Subordinated Indenture are hereinafter collectively referred
to as the "Indentures." Certain terms and provisions referred to in this
Prospectus or an applicable Prospectus Supplement as being part of the
Subordinated Indenture may instead be contained in the Corresponding
Subordinated Debt Security, a form of which will be filed with the Commission.
The following summary of certain provisions of the Indentures does not purport
to be complete and is qualified in its entirety by reference to the applicable
Indenture, which is filed as an exhibit to the Registration Statement. All
article and section references appearing herein are to articles and sections of
the applicable Indenture, and all capitalized terms have the meanings specified
in such Indenture. The Company expects that its subsidiaries will incur
additional liabilities from time to time. The Company may in the future issue
debt other than Debt Securities, which other debt may be secured or unsecured.
    
 
    The Company is principally a holding company whose primary sources of funds
are cash received from subsidiaries in the form of dividends and other
intercompany transfers of funds. As a holding company, the rights of any
creditors of the Company to participate in the assets of any subsidiary upon the
latter's liquidation or recapitalization will be subject to the prior claims of
the subsidiary's creditors, except to the extent that the Company may itself be
a creditor with recognized claims against the subsidiary. Accordingly, all Debt
Securities will effectively be subordinated to all existing and future
obligations of the Company's subsidiaries. At June 30, 1998, such liabilities of
the Company's subsidiaries aggregated $785 million (including $527 million of
Idaho Power Company first mortgage bonds), representing 100% of the aggregate
indebtedness of the Company and its consolidated subsidiaries.
 
                                       7

   
    Neither of the Indentures limits the amount of Debt Securities which may be
issued thereunder, and each Indenture provides that Debt Securities may be
issued thereunder up to the aggregate principal amount authorized from time to
time by the Company. The Indentures do not restrict the amount of other
unsecured or secured debt that may be incurred by the Company or any subsidiary.
The Indentures do not contain any covenant or other provision that is
specifically intended to afford any holder of Debt Securities special protection
in the event of highly leveraged transactions or any other transactions
resulting in a decline in the ratings or credit quality of the Company.
Reference is made to the Prospectus Supplement which accompanies this Prospectus
for the following terms and other information to the extent applicable with
respect to the Debt Securities being offered thereby: (i) the title of the
series being offered thereby, aggregate principal amount of such series,
authorized denominations and priority of such Debt Securities; (ii) the date or
dates on which such Debt Securities will mature (the "Stated Maturity"); (iii)
the rate or rates per annum at which such Debt Securities will bear interest, if
any, or the method of determination of such rate or rates; (iv) the dates on
which such interest, if any, will be payable and record dates, if any, for such
payment dates; (v) any provisions relating to the deferral of payment of any
interest; (vi) whether such Debt Securities are to be issued in whole or in part
in the form of one or more Global Securities and, if so, the identity of a
depository (the "Depository") for such Global Security or Securities; (vii) any
redemption or sinking fund provisions; (viii) the place or places of payment of
the principal of and any premium and interest on such Debt Securities (the
"Place of Payment"); and (ix) any additional or other rights, preferences,
privileges, limitations and restrictions relating to such Debt Securities.
    
 
    Unless otherwise specified in the applicable Prospectus Supplement, the Debt
Securities will be issued in fully registered form in denominations of $1000 and
integral multiples thereof (Section3.2). In addition, Debt Securities of a
series may be issuable in the form of one or more Global Securities, which will
be denominated in an amount equal to all or a portion of the aggregate principal
amount of such Debt Securities (Section2.4). See "--Global Debt Securities"
below.
 
    One or more series of Debt Securities may be sold at a substantial discount
below their stated principal amount, bearing no interest or interest at a rate
which at the time of issuance is below market rates. United States Federal
income tax consequences and special considerations applicable to any such series
will be described in the Prospectus Supplement relating thereto.
 
GLOBAL DEBT SECURITIES
 
    The Debt Securities of a series may be issued in whole or in part in the
form of one or more Global Securities that will be deposited with, or on behalf
of, the Depository identified in the Prospectus Supplement relating to such
series. Unless and until it is exchanged in whole or in part for Debt Securities
in individually certificated form, a Global Security may not be transferred
except as a whole to a nominee of the Depository for such Global Security, or by
a nominee of such Depository to such Depository, or to a successor of such
Depository or a nominee of such successor (Section2.4).
 
    So long as the Depository for a Global Debt Security, or its nominee, is the
registered owner of such Global Preferred Security, such Depository or such
nominee, as the case may be, will be considered the sole owner or holder of the
Debt Securities represented by such Global Debt Security for all purposes under
the Indenture governing such Debt Securities. Except as provided below, owners
of beneficial interests in a Global Debt Security will not be entitled to have
any of the individual Debt Securities of the series represented by such Global
Debt Security registered in their names, will not receive or be entitled to
receive physical delivery of any such Debt Securities of such series in
definitive form and will not be considered the owners or holders thereof under
the Indenture governing such Debt Securities.
 
    Payments of principal of and premium, if any, and interest on individual
Securities represented by a Global Debt Security registered in the name of a
Depository or its nominee will be made to the Depository
 
                                       8

or its nominee, as the case may be, as the registered owner of the Global Debt
Security representing such Debt Securities. None of the Company, the Trustee
under the Indenture governing such Debt Securities, any paying agent or
registrar for such Debt Securities will have any responsibility or liability for
any aspect of the records relating to or payments made on account of beneficial
ownership interests of the Global Debt Security representing such Debt
Securities or for maintaining, supervising or reviewing any records relating to
such beneficial ownership interests (Section8.3).
 
    For a description of the depository arrangements, see "Book-Entry Issuance."
Any additional terms of the depository arrangement with respect to any series of
Debt Securities and the rights of and limitations on owners of beneficial
interests in a Global Security representing all or a portion of a series of Debt
Securities may be described in the Prospectus Supplement relating to such
series.
 
MODIFICATION OF INDENTURES
 
   
    Each Indenture, the rights and obligations of the Company thereunder and the
rights of the holders of one or more series of Debt Securities issued under such
Indenture may be modified without the consent of the holders as to matters which
do not materially adversely affect the interests of the holders and, as to other
matters, with the consent of the holders of not less than a majority of the
aggregate principal amount of Debt Securities at the time Outstanding of all
series affected by the modification (voting as one class). Without the consent
of the holder of each Debt Security affected, however, no modification shall
change the maturity date of any such Debt Security, reduce the principal amount
or the amount of any premium payable thereon, reduce the rate, extend the time
of payment or change the method of calculation of interest thereon or reduce any
amount payable on redemption thereof or reduce the percentage required for any
such modification (Section10.2). No modification of the Senior Indenture
subordinating the indebtedness evidenced by any series of Senior Debt Securities
issued thereunder to any other indebtedness of the Company is effective against
any holder of a Senior Debt Security issued thereunder without his consent. No
modification of the Subordinated Indenture subordinating the indebtedness
evidenced by any series of Subordinated Debt Securities issued thereunder to any
indebtedness of the Company other than Senior Indebtedness is effective against
any holder of Subordinated Debt Securities without his consent. In addition, in
the case of Corresponding Subordinated Debt Securities, so long as any of the
Related Preferred Securities remain outstanding, no modification of the
applicable Subordinated Indenture may be made that adversely affects the holders
of such Preferred Securities in any material respect, and no defeasance of the
Subordinated Indenture may occur with respect to such Corresponding Debt
Securities, and no waiver of any Event of Default with respect to such
Corresponding Subordinated Debt Securities or waiver of compliance with any
covenant under the Subordinated Indenture applicable to such Corresponding Debt
Securities may be effective, without the prior consent of not less than a
majority of the aggregate liquidation amount of such related Preferred
Securities, and where consent under the Subordinated Indenture is not effective
against any holder without his consent, no such consent shall be given by the
Property Trustee without the prior consent of each holder of related Preferred
Securities (SectionSection6.10 and 10.2). See "--Certain Provisions Relating to
Corresponding Subordinated Debt Securities."
    
 
EVENTS OF DEFAULT
 
    Each Indenture provides that the following are Events of Default thereunder
with respect to any series of Debt Securities issued thereunder: (i) default in
the payment of the principal of, or premium, if any, on any Debt Security of
such series when and as the same shall be due and payable; (ii) default in
making a sinking fund payment, if any, when and as the same shall be due and
payable by the terms of any Debt Security of such series; (iii) default for 30
days in the payment of any installment of interest on any Debt Security of such
series and the time for payment has not been extended or deferred; (iv) default
for 60 days after written notice (given to the Company by the appropriate
Indenture Trustee or by the holders
 
                                       9

of at least 25% in aggregate principal amount of the Debt Securities then
Outstanding of all series affected) in the performance of any other covenant or
agreement in respect of the Debt Securities of such series contained in the
relevant Indenture; or (v) certain events of bankruptcy, insolvency or
reorganization, or any related court appointment of a receiver, liquidator or
trustee of the Company or for any substantial part of its property. (Section6.1)
An Event of Default with respect to the Debt Securities of any series does not
necessarily constitute an Event of Default with respect to any other series of
Debt Securities issued under such Indenture. The relevant Indenture Trustee is
required to give notice of any default known to it with respect to a series of
Debt Securities to the holders of Debt Securities of such series within ninety
(90) days of the occurrence thereof (unless such default is cured), provided
that such Indenture Trustee may withhold notice to the holders of the Debt
Securities of such series of any default with respect to the Debt Securities of
such series (except a default in the payment of principal, premium, if any, or
interest) if it considers such withholding to be in the interest of such holders
(Section6.11).
 
    In the case of an Event of Default relating to certain events of bankruptcy,
insolvency or reorganization, or any related court appointment of a receiver,
liquidator or trustee of the Company or for any substantial part of its
property, all Outstanding Debt Securities and interest accrued thereon, if any,
shall immediately become due and payable without declaration, presentment,
demand or notice of any kind by the Indenture Trustee or any holder of a Debt
Security. If any other Event of Default with respect to the Debt Securities of
such series shall have occurred and be continuing, the respective Indenture
Trustee or the holders of not less than 25% in aggregate principal amount of the
Outstanding Debt Securities of such series (or, in the case of certain Events of
Default that affect all series of Debt Securities then Outstanding, the holders
of not less than 25% in aggregate principal amount of all the Debt Securities
then outstanding treated as one class) may declare the principal, or in the case
of discounted Debt Securities of such series, such portion thereof as may be
described in the applicable Prospectus Supplement, of all the Debt Securities of
such series and interest accrued thereon, if any, to be due and payable
immediately. Subject to certain conditions, any acceleration of the Debt
Securities of any series may be rescinded and annulled by the holders of not
less than a majority in aggregate principal amount of the Outstanding Debt
Securities of such series (Section6.1).
 
    Within four months after the close of each year the Company must file with
the appropriate Indenture Trustee a certificate, signed by specified officers,
stating whether or not such officers have knowledge of any default relating to
its covenants, agreements and obligations contained in the relevant Indenture,
and, if so, specifying each such default and the nature thereof (Section4.6).
 
    Subject to provisions relating to its duties during the continuance of any
Event of Default, the Indenture Trustee shall be under no obligation to exercise
any of its rights or powers under the relevant Indenture at the request, order
or direction of any holders of Debt Securities, unless such holders shall have
offered to such Indenture Trustee reasonable indemnity (Section7.2). Subject to
such provisions for indemnification and subject to the right of the Indenture
Trustee to decline to follow any holders' directions under specified
circumstances, the holders of a majority in aggregate principal amount of the
Outstanding Debt Securities of such series may direct the time, method and place
of conducting any proceeding or any remedy available to such Indenture Trustee,
or exercising any trust or power conferred upon the Indenture Trustee, with
respect to the Debt Securities of such series (Section6.9).
 
CONSOLIDATION, MERGER OR SALE
 
    Each Indenture provides that the Company will not consolidate with or merge
into any other corporation, or sell, transfer or lease its properties as an
entirety or substantially as an entirety unless (i) the successor corporation,
if other than the Company, assumes in writing all of the terms, covenants and
conditions of the Indenture to be performed or observed by the Company,
including the due and punctual payment of the principal of, and premium, if any,
and interest, if any, on the Debt Securities issued
 
                                       10

thereunder and (ii) immediately after giving effect to such transaction, no
Event of Default and no event which after notice or lapse of time or both would
become an Event of Default shall have occurred and be continuing and the Company
shall have furnished the Indenture Trustee an officers' certificate and opinion
of counsel stating that the foregoing covenants have been complied with
(Section11.2).
 
TRANSFER
 
    Debt Securities may be registered for transfer or exchanged at the Corporate
Trust Office of the Indenture Trustee under the applicable Indenture or at any
other office or agency maintained by the Company for such purposes, subject to
the limitations in the applicable Indenture, without the payment of any service
charge except for any tax or governmental charge incidental thereto. Provisions
with respect to the transfer and exchange of Debt Securities in global form will
be set forth in the applicable Prospectus Supplement (Section3.6).
 
    The Company is not required to issue, exchange or register the transfer of
any Debt Securities during a period beginning at the opening of business 15 days
before the mailing of a notice of redemption and ending at the close of business
on the day of such mailing, or to exchange or register the transfer of the Debt
Securities selected, called or being called for redemption except, in the case
of Debt Securities to be redeemed in part, the portion thereof not to be
redeemed (Section3.6).
 
DEFEASANCE
 
    Except as otherwise provided with respect to the Debt Securities of any
series, each Indenture provides that the Company shall be discharged from its
obligations under such Indenture with respect to any series of Debt Securities
issued thereunder at any time prior to the maturity date or redemption thereof
when (a) the Company has irrevocably deposited with the applicable Indenture
Trustee, in trust, (i) sufficient funds to pay the principal of (and premium, if
any), and interest to maturity date (or redemption) on, the Debt Securities of
such series, or (ii) such amount of direct obligations of, or obligations the
principal of and interest on which are fully guaranteed by, the United States
Government, and which are not subject to prepayment, redemption or call, as
will, together with the predetermined and certain income to accrue thereon
without consideration of any reinvestment thereof, be sufficient to pay when due
the principal of (and premium, if any), and interest to maturity date (or
redemption) on, the Debt Securities of such series, and (b) the Company has paid
all other sums payable with respect to the Debt Securities of such series. Upon
such discharge, the holders of the Debt Securities of such series shall no
longer be entitled to the benefits of the applicable Indenture, except for the
purposes of registration of transfer and exchange of the Debt Securities of such
series, and replacement of lost, stolen or mutilated Debt Securities of such
series (SectionSection12.1 and 12.3).
 
PAYMENT AND PAYING AGENT
 
    Unless otherwise indicated in the applicable Prospectus Supplement, payment
of the interest on a Debt Security on any Interest Payment Date will be made to
the Person in whose name such Debt Security (or one or more predecessor Debt
Securities) is registered at the close of business on the applicable record date
for the payment of such interest (Section3.8).
 
    Principal of and any premium and interest on the Debt Securities of a
particular series will be payable at the office of such Paying Agent or Paying
Agents as the Company may designate with respect to the Debt Securities of such
series for such purpose from time to time, except that unless otherwise
indicated in the applicable Prospectus Supplement, payment of any interest may
be made by check mailed to the address of the Person entitled thereto as such
address appears in the Security Register. Unless otherwise
 
                                       11

indicated in the applicable Prospectus Settlement, the corporate trust office of
the Trustee in The City of New York will be designated as the Company's sole
Paying Agent for payments with respect to Debt Securities of each series. Any
other Paying Agents initially designated by the Company for the Debt Securities
of a particular series will be named in the applicable Prospectus Supplement.
The Company will be required to maintain a Paying Agent in each Place of Payment
for the Debt Securities of a particular series. (SectionSection4.1 and 4.2.)
 
    All moneys paid by the Company to a Paying Agent for the payment of their
principal of or any premium or interest on any Debt Security which remains
unclaimed at the end of two years after such principal, premium or interest has
become due and payable will be repaid to the Company, and the holder of such
Debt Security thereafter may look only to the Company for payment thereof.
(Section12.5.)
 
SENIOR DEBT SECURITIES--SENIOR INDEBTEDNESS
 
   
    The Senior Debt Securities will rank PARI PASSU with all outstanding
unsecured debt of the Company that is not subordinated by its terms and will
constitute part of the Senior Indebtedness for purposes of the Subordinated
Indenture.
    
 
   
    The term "Senior Indebtedness" is defined to mean all Indebtedness of the
Company, unless, in the instrument creating or evidencing the same or pursuant
to which the same is outstanding, it is provided that such obligations are not
superior in right of payment to Subordinated Indebtedness or to other
Indebtedness of the Company which is PARI PASSU with, or subordinated to,
Subordinated Indebtedness. The term "Indebtedness" is defined to mean, with
respect to a Person, (i) the principal of and premium, if any, and interest, if
any, on, (A) indebtedness of such Person for money borrowed and (B) indebtedness
evidenced by securities, notes, debentures, bonds or other similar instruments
issued by such Person; (ii) all capital lease obligations of such Person; (iii)
all obligations of such Person issued or assumed as the deferred purchase price
of property, all conditional sale obligations of such Person and all obligations
of such Person under any conditional sale or title retention agreement (but
excluding trade accounts payable and accrued liabilities in the ordinary course
of business); (iv) all obligations, contingent or otherwise, of such Person in
respect of any letters of credit, banker's acceptances, security purchase
facilities or similar credit transactions; (v) all obligations in respect of
interest rate swap, cap, floor, collar or other agreements, interest rate future
or option contracts, currency swap agreements, currency or other future or
option contracts and other similar agreements; and (vi) all obligations of the
type referred to in clauses (i) through (v) of others for the payment of which
such Person is responsible or liable as obligor, guarantor or otherwise
(Section1.1 of the Subordinated Indenture). The amount of Senior Indebtedness
which the Company may issue is not subject to any limitation. The Senior
Indenture places no limitation on the amount of indebtedness, including without
limitation, secured debt, that may be incurred by the Company. In addition, the
Senior Indenture places no limitation on the obligations that may be incurred by
the Company's subsidiaries.
    
 
SUBORDINATED DEBT SECURITIES--SUBORDINATION
 
    The Subordinated Debt Securities will constitute part of the Subordinated
Indebtedness of the Company and will be subordinate and subject in right of
payment to the prior payment in full of all Senior Indebtedness of the Company,
whether outstanding at the date of the Subordinated Indenture or incurred after
such date.
 
    In the event of (i) any insolvency, bankruptcy, receivership, liquidation,
reorganization, readjustment, composition or other similar proceeding relating
to the Company or its property, (ii) any proceeding for the liquidation,
dissolution or other winding up of the Company, voluntary or involuntary,
whether or not involving insolvency or bankruptcy proceedings, (iii) any
assignment by the Company for the benefit of
 
                                       12

creditors or (iv) any other marshalling of the assets of the Company, all Senior
Indebtedness (including any interest thereon accruing after the commencement of
any such proceedings) shall first be paid in full before any payment or
distribution, whether in cash, securities or other property, shall be made on
account of the principal of and the premium, if any, or interest on the
Subordinated Debt Securities. In such event, any payment or distribution on
account of the principal of or premium, if any, or interest on the Subordinated
Debt Securities, whether in cash, securities or other property (other than
securities of the Company or any other corporation provided for by a plan of
reorganization or readjustment the payment of which is subordinate, at least to
the extent provided in the subordination provisions with respect to the
Subordinated Debt Securities, to the payment of all Senior Indebtedness at the
time outstanding, and to any securities issued in respect thereof under any such
plan of reorganization or readjustment), which would otherwise (but for the
subordination provisions) be payable or deliverable in respect of the
Subordinated Debt Securities shall be paid or delivered directly to the holders
of Senior Indebtedness in accordance with the priorities then existing among
such holders until all Senior Indebtedness (including any interest thereon
accruing after the commencement of any such proceedings) shall have been paid in
full. (Section16.2)
 
    In the event of any such proceeding, after payment in full of all sums owing
with respect to Senior Indebtedness, the holders of Subordinated Debt
Securities, together with the holders of any obligations of the Company ranking
on a parity with the Subordinated Debt Securities, shall be entitled to be paid
from the remaining assets of the Company the amounts at any time due and owing
on account of unpaid principal of and premium, if any, and interest on the
Subordinated Debt Securities and such other obligations before any payment or
other distribution, whether in cash, property or otherwise, shall be made on
account of any capital stock or obligations of the Company ranking junior to the
Subordinated Debt Securities and such other obligations. If any payment or
distribution on account of the principal of or interest on the Subordinated Debt
Securities of any character or any security, whether in cash, securities or
other property (other than securities of the Company or any other corporation
provided for by a plan of reorganization or readjustment the payment of which is
subordinate, at least to the extent provided in the subordination provisions
with respect to the Subordinated Debt Securities, to the payment of all Senior
Indebtedness at the time outstanding and to any securities issued in respect
thereof under any such plan of reorganization or readjustment) shall be received
by any holder of any Subordinated Debt Securities in contravention of any of the
terms hereof and before all the Senior Indebtedness shall have been paid in
full, such payment or distribution or security shall be received in trust for
the benefit of, and shall be paid over or delivered and transferred to, the
holders of the Senior Indebtedness at the time outstanding in accordance with
the priorities then existing among such holders for application to the payment
of all Senior Indebtedness remaining unpaid to the extent necessary to pay all
such Senior Indebtedness in full. By reason of such subordination, in the event
of the insolvency of the Company, holders of Senior Indebtedness may receive
more, ratably, and holders of the Subordinated Debt Securities having a claim
pursuant to such securities may receive less, ratably, than the other creditors
of the Company. Such subordination will not prevent the occurrence of any Event
of Default in respect of the Subordinated Debt Securities.
 
   
    The Subordinated Indenture places no limitation on the amount of additional
Senior Indebtedness that may be incurred by the Company or on obligations that
may be incurred by the Company's subsidiaries. The Company expects from time to
time to incur additional indebtedness constituting Senior Indebtedness.
    
 
    The Subordinated Indenture provides that the foregoing subordination
provisions, insofar as they relate to any particular series of Subordinated Debt
Securities, may be changed prior to the issuance of such series. Any such change
would be described in the applicable Prospectus Supplement.
 
                                       13

CERTAIN PROVISIONS RELATING TO CORRESPONDING SUBORDINATED DEBT SECURITIES
 
    GENERAL.  The Corresponding Subordinated Debt Securities may be issued in
one or more series of Subordinated Debt Securities under the Subordinated
Indenture with terms corresponding to the terms of a series of related Preferred
Securities issued by an IDACORP Trust. Concurrently with the issuance of the
IDACORP Trust's Preferred Securities, such IDACORP Trust will invest the
proceeds thereof and the consideration paid by the Company for the Common
Securities in a series of Corresponding Subordinated Debt Securities issued by
the Company to such IDACORP Trust. Each series of Corresponding Subordinated
Debt Securities will be in the principal amount equal to the aggregate stated
Liquidation Amount of the related Preferred Securities and the Common Securities
of such IDACORP Trust and will rank PARI PASSU with all other series of
Subordinated Debt Securities. Holders of the related Preferred Securities for a
series of Corresponding Subordinated Debt Securities will have the rights in
connection with modifications to the Subordinated Indenture or upon occurrence
of a Trust Event of Default relating to Corresponding Subordinated Debt
Securities described under "--Modification of Indentures," and "--Events of
Default," and under "--Enforcement of Certain Rights by Holders of Preferred
Securities" below, unless provided otherwise in the Prospectus Supplement for
such related Preferred Securities.
 
    The Company will covenant, as to each series of Corresponding Subordinated
Debt Securities, (i) to maintain directly or indirectly 100% ownership of the
Common Securities of the IDACORP Trust to which such Corresponding Subordinated
Debt Securities have been issued, provided that certain successors which are
permitted pursuant to the Subordinated Indenture may succeed to the Company's
ownership of the Common Securities, (ii) not to voluntarily dissolve, wind-up or
liquidate any IDACORP Trust, except (a) in connection with a distribution of
Corresponding Subordinated Debt Securities to the holders of the Preferred
Securities in liquidation of such IDACORP Trust or (b) in connection with
certain mergers, consolidations or amalgamations permitted by the related Trust
Agreement and (iii) to use its reasonable efforts, consistent with the terms and
provisions of the related Trust Agreement, to cause such IDACORP Trust to remain
classified as a grantor trust and not as an association taxable as a corporation
for United States Federal income tax purposes. For additional covenants relating
to payment of certain expenses of the IDACORP Trusts, see "Description of
Preferred Securities--Payment of Expenses."
 
    OPTION TO EXTEND INTEREST PAYMENT DATE.  If provided in the applicable
Prospectus Supplement, the Company shall have the right at any time and from
time to time during the term of any series of Corresponding Subordinated Debt
Securities to defer payment of interest for such number of consecutive interest
payment periods as may be specified in the applicable Prospectus Supplement
(each, an "Extension Period"), subject to the terms, conditions and covenants,
if any, specified in such Prospectus Supplement, provided that such Extension
Period may not extend beyond the maturity date of such series of Corresponding
Subordinated Debt Securities. Certain United States Federal income tax
consequences and special considerations applicable to any such Corresponding
Subordinated Debt Securities will be described in the applicable Prospectus
Supplement (Section3.12 of the Subordinated Indenture).
 
    REDEMPTION.  Unless otherwise indicated in the applicable Prospectus
Supplement, the Company may, at its option, redeem the Corresponding
Subordinated Debt Securities of any series in whole at any time or in part from
time to time. Corresponding Subordinated Debt Securities may be redeemed in the
denominations as set forth in the applicable Prospectus Supplement. Except as
otherwise specified in the applicable Prospectus Supplement, the redemption
price for any Corresponding Subordinated Debt Security so redeemed shall equal
any accrued and unpaid interest thereon to the redemption date, plus the
principal amount thereof. Unless otherwise specified in the applicable
Prospectus Supplement, the Company may not redeem a series of Corresponding
Subordinated Debt Securities in part unless all accrued and unpaid interest has
been paid in full on all outstanding Corresponding Subordinated Debt Securities
of such series for all interest periods terminating on or prior to the date
fixed for redemption.
 
                                       14

   
    Except as otherwise specified in the applicable Prospectus Supplement, if a
Subordinated Debt Security Tax Event (as defined below) or an Investment Company
Event (as defined below) in respect of an IDACORP Trust shall occur and be
continuing, the Company may, at its option, redeem the Corresponding
Subordinated Debt Securities held by such IDACORP Trust at any time within 90
days of the occurrence of such Subordinated Debt Security Tax Event or
Investment Company Event, in whole but not in part, subject to the provisions of
the Subordinated Indenture. Unless otherwise specified in the applicable
Prospectus Supplement, the redemption price for any such Corresponding
Subordinated Debt Securities shall be equal to 100% of the principal amount of
such Corresponding Subordinated Debt Securities then outstanding plus accrued
and unpaid interest to the date fixed for redemption. For so long as the
applicable IDACORP Trust is the holder of all such outstanding Corresponding
Subordinated Debt Securities, the proceeds of any such redemption will be used
by the IDACORP Trust to redeem the corresponding Trust Securities in accordance
with their terms (Section14.4 of the Subordinated Indenture).
    
 
    "Subordinated Debt Security Tax Event" means the receipt by the applicable
IDACORP Trust of an opinion of counsel experienced in such matters to the effect
that, as a result of any amendment to, or change (including any announced
proposed change) in, the laws (or any regulations thereunder) of the United
States or any political subdivision or taxing authority thereof or therein, or
as a result of any official administrative written decision, pronouncement or
action or judicial decision interpreting or applying such laws or regulations,
which amendment or change is effective or which proposed change, pronouncement,
action or decision is announced on or after the date of issuance of the
applicable series of Corresponding Subordinated Debt Securities, there is more
than an insubstantial risk that (i) the applicable IDACORP Trust is, or will be
within 90 days of the date of such opinion, subject to United States Federal
income tax with respect to income received or accrued on the corresponding
series of Corresponding Subordinated Debt Securities, (ii) interest payable by
the Company on such series of Corresponding Subordinated Debt Securities is not,
or within 90 days of the date of such opinion, will not be, deductible by the
Company, in whole or in part, for United States Federal income tax purposes or
(iii) the applicable IDACORP Trust is, or will be within 90 days of the date of
such opinion, subject to more than a DE MINIMIS amount of other taxes, duties or
other governmental charges (Section1.1 of the Subordinated Indenture).
 
    "Investment Company Event" means the receipt by the applicable IDACORP Trust
of an opinion of counsel experienced in such matters to the effect that, as a
result of the occurrence of a change in law or regulation or a change in
interpretation or application of law or regulation by any legislative body,
court, governmental agency or regulatory authority (a "Change in the Investment
Company Act"), the applicable IDACORP Trust is or will be considered an
"investment company" that is required to be registered under the Investment
Company Act of 1940, as amended (the "Investment Company Act"), which Change in
the Investment Company Act becomes effective on or after the date of original
issuance of the series of Preferred Securities issued by the IDACORP Trust
(Section1.1 of the Subordinated Indenture).
 
    RESTRICTIONS ON CERTAIN PAYMENTS.  The Company will, unless otherwise
provided in the applicable Prospectus Supplement, covenant, as to each series of
Corresponding Subordinated Debt Securities, that it will not (i) declare or pay
any dividends or distributions on, or redeem, purchase, acquire, or make a
liquidation payment with respect to, any of the Company's capital stock or (ii)
make any payment of principal, interest or premium, if any, on or repay or
repurchase or redeem any debt securities of the Company (including other
Corresponding Subordinated Debt Securities) that rank PARI PASSU with or junior
in interest to the Corresponding Subordinated Debt Securities or make any
guarantee payments with respect to any guarantee by the Company of the debt
securities of any subsidiary of the Company if such guarantee ranks PARI PASSU
with or junior in interest to the Corresponding Subordinated Debt Securities
(other than (a) dividends or distributions in common stock of the Company, (b)
redemptions or purchases of any rights pursuant to the Company's Rights
Agreement, or any successor to such Rights Agreement, and the declaration of a
dividend of such rights or the issuance of stock under such plans in the future,
(c) payments under any Guarantee and (d) purchases of common stock related to
the issuance
 
                                       15

of common stock under the Company's Dividend Reinvestment and Stock Purchase
Plan or under any of the Company's benefit plans for its directors, officers or
employees) if at such time (A) there shall have occurred any event of which the
Company has actual knowledge (a) that with the giving of notice or the lapse of
time, or both, would constitute an Event of Default under the Subordinated
Indenture with respect to the Corresponding Subordinated Debt Securities of such
series and (b) in respect of which the Company shall not have taken reasonable
steps to cure, (B) if such Corresponding Subordinated Debt Securities are held
by an IDACORP Trust which is the issuer of a series of related Preferred
Securities, the Company shall be in default with respect to its payment of any
obligations under the Guarantee relating to such Preferred Securities or (C) the
Company shall have given notice of its selection of an Extension Period as
provided pursuant to the Subordinated Indenture with respect to the
Corresponding Subordinated Debt Securities of such series and shall not have
rescinded such notice, or such Extension Period, or any extension thereof, shall
be continuing (Section4.8 of the Subordinated Indenture).
 
    ENFORCEMENT OF CERTAIN RIGHTS BY HOLDERS OF PREFERRED SECURITIES.  If an
Event of Default with respect to a series of Corresponding Subordinated Debt
Securities has occurred and is continuing and such event is attributable to the
failure of the Company to pay principal of or premium, if any, or interest, if
any, on such series of Corresponding Subordinated Debt Securities on the date
such interest, premium or principal is otherwise payable, a holder of related
Preferred Securities may institute a legal proceeding directly against the
Company for enforcement of payment to such holder of the principal of or
premium, if any, or interest, if any, on such Corresponding Subordinated Debt
Securities having a principal amount equal to the aggregate Liquidation Amount
of the related Preferred Securities of such holder. The holder of at least a
majority in aggregate liquidation amount of Preferred Securities of the Trust
must consent to any waiver of an Event of Default with respect to the series of
Subordinated Debt Securities held by the Trust and each such holder must consent
to any supplemental indenture that would adversely affect the interests of such
holders. (SectionSection6.1, 6.7 and 10.2 of the Subordinated Indenture)
 
CONCERNING THE INDENTURE TRUSTEES
 
    Business and other relationships (including other trusteeships), if any,
between the Company and its affiliates, on the one hand, and the Indenture
Trustee, on the other hand, under the Indenture pursuant to which the Debt
Securities of a series are issued will be described in the Prospectus Supplement
relating to such Debt Securities.
 
    In the event Debt Securities are issued pursuant to an Indenture with an
Indenture Trustee which is also an Indenture Trustee for any subordinate or
superior class of Debt Securities pursuant to an Indenture, the occurrence of
any default under either Indenture could create a conflicting interest for the
respective Indenture Trustee under the Trust Indenture Act. If such default has
not been cured or waived within 90 days after such Indenture Trustee has or
acquires a conflicting interest, such Indenture Trustee generally is required by
the Trust Indenture Act to eliminate such conflicting interest or resign as
Indenture Trustee with respect to the Debt Securities issued under one such
Indenture. In the event of the Indenture Trustee's resignation, the Company
shall promptly appoint a successor trustee with respect to the affected Debt
Securities.
 
                                       16

                       DESCRIPTION OF THE PREFERRED STOCK
 
   
    The following description is a summary of certain provisions of the
Preferred Stock and does not purport to be complete and is subject to, and is
qualified in its entirety by reference to, the Company's Amended Bylaws (the
"Bylaws"), the Company's Articles of Incorporation, as amended (the "Articles"),
and the Articles of Amendment (the "Articles of Amendment") with respect to each
such series adopted by the Board of Directors (the "Board of Directors") of the
Company, which will be filed with the Commission in connection with the offering
of such series of Preferred Stock, and the laws of the State of Idaho. The
Prospectus Supplement relating to an offering of Preferred Stock will describe
terms relevant thereto including, without limitation, the number of shares
offered, the initial offering price and dividend information.
    
 
GENERAL
 
   
    Pursuant to the Company's Articles, the Company is authorized to issue up to
20,000,000 shares of Preferred Stock, without par value, of which 18,800,000
shares are available for issuance as of the date of this Prospectus. The
Preferred Stock is issuable from time to time in one or more series and with
such designations and preferences for each series as shall be stated in the
Articles of Amendment providing for the designation and issue of each such
series adopted by the Board of Directors of the Company. The Board of Directors
is authorized by the Company's Articles to determine the voting, dividend,
redemption and liquidation preferences and limitations pertaining to such
series. Holders of Preferred Stock have no right to vote except as otherwise
provided by law or as may be established by the Board of Directors. The Board of
Directors has the full authority to determine the terms of any series of
Preferred Stock and to issue Preferred Stock with voting and other rights that
could adversely affect the voting power of the holders of the Common Stock and
could have certain anti-takeover effects. The ability of the Board of Directors
to issue Preferred Stock without stockholder approval could have the effect of
delaying, deferring or preventing a change in control of the Company or the
removal of existing management. See "Certain Matters That May Have an
Anti-Takeover Effect--Provisions of the Company's Articles of Incorporation, as
amended and Amended Bylaws" below.
    
 
    Any Preferred Stock offered hereby will have the dividend, liquidation and
voting rights set forth below unless otherwise provided in the Articles of
Amendment, and described in the Prospectus Supplement relating to a particular
series of Preferred Stock. Reference is made to the Prospectus Supplement
relating to the particular series of Preferred Stock offered thereby for
specific terms, including: (i) the number of shares constituting such series and
the designation thereof; (ii) the rate or rates of dividend, if any, or any
formula or other method or other means by which such rate or rates are to be
determined at any time or from time to time, the date or dates on which
dividends may be payable, whether such dividends shall be cumulative,
noncumulative or partially cumulative and, if cumulative or partially
cumulative, the date from which dividends shall accumulate; (iii) whether shares
may be redeemed or converted (a) at the option of the Company, the shareholder
or another person or upon the occurrence of a designated event; (b) for cash,
indebtedness, securities or other property; (c) in a designated amount or in an
amount determined in accordance with a designated formula or by reference to
extrinsic data or events; (iv) the preference, if any, of shares of such series
over any other class of shares with respect to distributions, including
dividends and distributions upon any voluntary or involuntary dissolution,
liquidation or winding up of the Company; (v) whether the shares shall have any
voting powers, in addition to the voting powers provided by law, and the terms
of any such voting powers; and (vi) any other relative rights, preferences and
limitations of that series.
 
    As described under "Description of Depository Shares", the Company may, at
its option, elect to offer depository shares ("Depository Shares") evidenced by
depository receipts ("Depository Receipts"), each representing an interest (to
be specified in the Prospectus Supplement relating to the particular series of
the Preferred Stock) in a share of the particular series of the Preferred Stock
issued and deposited with a Preferred Stock Depository (as defined herein).
 
                                       17

    The Company does not currently have any shares of Preferred Stock
outstanding. However, the Board of Directors has reserved 1,200,000 shares of
Preferred Stock for issuance in connection with the Rights Plan described below.
See "Certain Matters That May Have an Anti-Takeover Effect--Rights Plan." The
Preferred Stock offered hereby will be issued in one or more series. The holders
of Preferred Stock will have no preemptive rights. Preferred Stock will be fully
paid and nonassessable upon issuance against full payment of the purchase price
therefor. Unless otherwise specified in the Articles of Amendment, and described
in the Prospectus Supplement relating to a particular series of Preferred Stock,
each series of Preferred Stock will, with respect to dividend rights and rights
on liquidation, dissolution and winding up of the Company, rank prior to the
Common Stock (the "Junior Stock") and on a parity with each other series of
Preferred Stock offered hereby (the "Parity Stock").
 
DIVIDEND RIGHTS
 
    Holders of the Preferred Stock may be entitled to receive, when, as and if
declared by the Board of Directors of the Company, out of funds legally
available therefor, cash dividends at such rates and on such dates as are set
forth in the Articles of Amendment, and described in the Prospectus Supplement,
relating to such series of Preferred Stock. Such rate may be fixed or variable
or both. Each such dividend will be payable to the holders of record as they
appear on the stock record books of the Company on such record dates as may be
fixed by the Board of Directors of the Company. Dividends on any series of the
Preferred Stock may be cumulative, partially cumulative or noncumulative, as
provided in the Articles of Amendment, and described in the Prospectus
Supplement, relating thereto. If the Board of Directors of the Company fails to
declare a dividend payable on a dividend payment date on any series of Preferred
Stock for which dividends are noncumulative, then the right to receive a
dividend in respect of the dividend period ending on such dividend payment date
will be lost, and the Company will have no obligation to pay the dividend
accrued for such period, whether or not dividends on such series are declared
for any future period. Dividends on shares of each series of Preferred Stock for
which dividends are cumulative will accrue from the date set forth in the
Articles of Amendment, and described in the applicable Prospectus Supplement,
relating to such series.
 
    The Preferred Stock of each series may include customary provisions (i)
restricting the payment of dividends or the making of other distributions on, or
the redemption, purchase or other acquisition of, Junior Stock unless full
dividends, including, in the case of cumulative Preferred Stock, accruals, if
any, in respect of prior dividend periods, on the shares of such series of
Preferred Stock have been paid and (ii) providing for the PRO RATA payment of
dividends on such series and other Parity Stock when dividends have not been
paid in full upon such series and other Parity Stock.
 
VOTING RIGHTS
 
    The holders of Preferred Stock of a series offered hereby will not be
entitled to vote except as provided in the Articles of Amendment and indicated
in the Prospectus Supplement relating to such series of Preferred Stock, or as
required by applicable law.
 
REDEMPTION
 
    The Company will have such rights, if any, to redeem shares of Preferred
Stock, and the holders of Preferred Stock will have such rights, if any, to
cause the Company to redeem shares of Preferred Stock, as may be set forth in
the Articles of Amendment, and described in the Prospectus Supplement, relating
to a series of Preferred Stock.
 
CONVERSION OR EXCHANGE
 
    The terms, if any, on which Preferred Stock of a series will be convertible
into or exchangeable for Common Stock, other securities, property, cash or
obligations, or a combination of any of the foregoing,
 
                                       18

will be summarized in the Prospectus Supplement relating to such series. Such
terms may include provisions for conversion or exchange, either on a mandatory
basis, at the option of the holder or at the option of the Company. The number
of shares of Common Stock, other securities, or the property, cash or
obligations, to be received by the holders of a series of Preferred Stock upon
conversion or exchange will be calculated according to the factors and at such
time as is summarized in the related Prospectus Supplement.
 
RIGHTS UPON LIQUIDATION
 
    In the event of any voluntary or involuntary liquidation, dissolution or
winding up of the Company, the holders of each series of Preferred Stock will be
entitled to receive out of assets of the Company available for distribution to
stockholders, before any distribution of assets is made to holders of Junior
Stock, liquidating distributions in the amount set forth in the Articles of
Amendment, and described in the Prospectus Supplement, relating to such series
of Preferred Stock plus an amount equal to accrued and unpaid dividends. If,
upon any voluntary or involuntary liquidation, dissolution or winding up of the
Company, the amounts payable with respect to the Preferred Stock of any series
are not paid in full, the holders of the Preferred Stock of such series will
share ratably in any such distribution of assets of the Company in proration to
the full respective preferential amounts (which may include accumulated
dividends) to which they are entitled. After payment of the full amount of the
liquidating distribution to which they are entitled, the holders of such series
of Preferred Stock will have no right or claim to any of the remaining assets of
the Company. Neither the sale of all or a portion of the Company's assets nor
the merger or consolidation of the Company into or with any other corporation
shall be deemed to be a dissolution, liquidation or winding up, voluntarily or
involuntarily, of the Company.
 
                        DESCRIPTION OF DEPOSITORY SHARES
 
    The description set forth below and in any Prospectus Supplement of certain
provisions of the Deposit Agreement (as defined below) and of the Depository
Shares and Depository Receipts summarizes the material terms of the Deposit
Agreement and of the Depository Shares and Depository Receipts, and is qualified
in its entirety by reference to, the form of Deposit Agreement and form of
Depository Receipts relating to each series of the Preferred Stock.
 
GENERAL
 
    The Company may, at its option, elect to have shares of Preferred Stock be
represented by Depository Shares. The shares of any series of the Preferred
Stock underlying the Depository Shares will be deposited under a separate
deposit agreement (the "Deposit Agreement") between the Company and a bank or
trust company selected by the Company (the "Preferred Stock Depository"). The
Prospectus Supplement relating to a series of Depository Shares will set forth
the name and address of the Preferred Stock Depository. Subject to the terms of
the Deposit Agreement, each owner of a Depository Share will be entitled,
proportionately, to all the rights, preferences and privileges of the Preferred
Stock represented thereby (including dividend, voting, redemption, conversion,
exchange and liquidation rights).
 
    The Depository Shares will be evidenced by Depository Receipts issued
pursuant to the Deposit Agreement, each of which will represent the applicable
interest in a number of shares of a particular series of the Preferred Stock
described in the applicable Prospectus Supplement.
 
    A holder of Depository Shares will be entitled to receive the shares of
Preferred Stock (but only in whole shares of Preferred Stock) underlying such
Depository Shares. If the Depository Receipts delivered by the holder evidence a
number of Depository Shares in excess of the whole number of shares of Preferred
Stock to be withdrawn, the Depository will deliver to such holder at the same
time a new Depository Receipt evidencing such excess number of Depository
Shares.
 
                                       19

DIVIDENDS AND OTHER DISTRIBUTIONS
 
    The Preferred Stock Depository will distribute all cash dividends or other
cash distributions in respect of the Preferred Stock to the record holders of
Depository Receipts in proportion, insofar as possible, to the number of
Depository Shares owned by such holders.
 
    In the event of a distribution other than in cash in respect of the
Preferred Stock, the Preferred Stock Depository will distribute property
received by it to the record holders of Depository Receipts in proportion,
insofar as possible, to the number of Depository Shares owned by such holders,
unless the Preferred Stock Depository determines that it is not feasible to make
such distribution, in which case the Preferred Stock Depository may, with the
approval of the Company, adopt such method as it deems equitable and practicable
for the purpose of effecting such distribution, including sale (at public or
private sale) of such property and distribution of the net proceeds from such
sale to such holders.
 
    The amount so distributed in any of the foregoing cases will be reduced by
any amount required to be withheld by the Company or the Preferred Stock
Depository on account of taxes.
 
CONVERSION AND EXCHANGE
 
    If any Preferred Stock underlying the Depository Shares is subject to
provisions relating to its conversion or exchange as set forth in the Prospectus
Supplement relating thereto, each record holder of Depository Shares will have
the right or obligation to convert or exchange such Depository Shares pursuant
to the terms thereof.
 
REDEMPTION OF DEPOSITORY SHARES
 
    If Preferred Stock underlying the Depository Shares is subject to
redemption, the Depository Shares will be redeemed from the proceeds received by
the Preferred Stock Depository resulting from the redemption, in whole or in
part, of the Preferred Stock held by the Preferred Stock Depository. The
redemption price per Depository Share will be equal to the aggregate redemption
price payable with respect to the number of shares of Preferred Stock underlying
the Depository Shares. Whenever the Company redeems Preferred Stock from the
Preferred Stock Depository, the Preferred Stock Depository will redeem as of the
same redemption date a proportionate number of Depository Shares representing
the shares of Preferred Stock that were redeemed. If less than all the
Depository Shares are to be redeemed, the Depository Shares to be redeemed will
be selected by lot or PRO RATA, as may be determined by the Company.
 
    After the date fixed for redemption, the Depository Shares so called for
redemption will no longer be deemed to be outstanding and all rights of the
holders of the Depository Shares will cease, except the right to receive the
redemption price upon such redemption. Any funds deposited by the Company with
the Preferred Stock Depository for any Depository Shares which the holders
thereof fail to redeem shall be returned to the Company after a period of two
years from the date such funds are so deposited.
 
VOTING
 
    Upon receipt of notice of any meeting at which the holders of any shares of
Preferred Stock underlying the Depository Shares are entitled to vote, the
Preferred Stock Depository will mail the information contained in such notice to
the record holders of the Depository Receipts. Each record holder of such
Depository Receipts on the record date (which will be the same date as the
record date for the Preferred Stock) will be entitled to instruct the Preferred
Stock Depository as to the exercise of the voting rights pertaining to the
number of shares of Preferred Stock underlying such holder's Depository Shares.
The Preferred Stock Depository will endeavor, insofar as practicable, to vote
the number of shares of Preferred Stock underlying such Depository Shares in
accordance with such instructions, and the Company will agree to take all
reasonable action which may be deemed necessary by the Preferred Stock
Depository
 
                                       20

in order to enable the Preferred Stock Depository to do so. The Preferred Stock
Depository will abstain from voting the Preferred Stock to the extent it does
not receive specific written instructions from holders of Depository Receipts
representing such Preferred Stock.
 
RECORD DATE
 
    Whenever (i) any cash dividend or other cash distribution shall become
payable, any distribution other than cash shall be made, or any rights,
preferences or privileges shall be offered with respect to the Preferred Stock,
or (ii) the Preferred Stock Depository shall receive notice of any meeting at
which holders of Preferred Stock are entitled to vote or of which holders of
Preferred Stock are entitled to notice, or of the mandatory conversion of or any
election on the part of the Company to call for the redemption of any Preferred
Stock, the Preferred Stock Depository shall in each such instance fix a record
date (which shall be the same as the record date for the Preferred Stock) for
the determination of the holders of Depository Receipts (x) who shall be
entitled to receive such dividend, distribution, rights, preferences or
privileges or the net proceeds of the sale thereof or (y) who shall be entitled
to give instructions for the exercise of voting rights at any such meeting or to
receive notice of such meeting or of such redemption or conversion, subject to
the provisions of the Deposit Agreement.
 
AMENDMENT AND TERMINATION OF THE DEPOSIT AGREEMENT
 
    The form of Depository Receipt and any provision of the Deposit Agreement
may at any time be amended by agreement between the Company and the Preferred
Stock Depository. However, any amendment which imposes or increases any fees,
taxes or other charges payable by the holders of Depository Receipts (other than
taxes and other governmental charges, fees and other expenses payable by such
holders as stated under "--Charges of Preferred Stock Depository"), or which
otherwise prejudices any substantial existing right of holders of Depository
Receipts, will not take effect as to outstanding Depository Receipts until the
expiration of 90 days after notice of such amendment has been mailed to the
record holders of outstanding Depository Receipts.
 
    Whenever so directed by the Company, the Preferred Stock Depository will
terminate the Deposit Agreement by mailing notice of such termination to the
record holders of all Depository Receipts then outstanding at least 30 days
prior to the date fixed in such notice for such termination. The Preferred Stock
Depository may likewise terminate the Deposit Agreement if at any time 45 days
shall have expired after the Preferred Stock Depository shall have delivered to
the Company a written notice of its election to resign and a successor
depository shall not have been appointed and accepted its appointment. If any
Depository Receipts remain outstanding after the date of termination, the
Preferred Stock Depository thereafter will discontinue the transfer of
Depository Receipts, will suspend the distribution of dividends to the holders
thereof, and will not give any further notices (other than notice of such
termination) or perform any further acts under the Deposit Agreement except as
provided below and except that the Preferred Stock Depository will continue (i)
to collect dividends on the Preferred Stock and any other distributions with
respect thereto and (ii) to deliver the Preferred Stock together with such
dividends and distributions and the net proceeds of any sales of rights,
preferences, privileges or other property, without liability for interest
thereon, in exchange for Depository Receipts surrendered. At any time after the
expiration of two years from the date of termination, the Preferred Stock
Depository may sell the Preferred Stock then held by it at public or private
sales, at such place or places and upon such terms as it deems proper and may
thereafter hold the net proceeds of any such sale, together with any money and
other property then held by it, without liability for interest thereon, for the
PRO RATA benefit of the holders of Depository Receipts which have not been
surrendered.
 
CHARGES OF PREFERRED STOCK DEPOSITORY
 
    The Company will pay all charges of the Preferred Stock Depository including
charges in connection with the initial deposit of the Preferred Stock, the
initial issuance of the Depository Receipts, the
 
                                       21

distribution of information to the holders of Depository Receipts with respect
to matters on which Preferred Stock is entitled to vote, withdrawals of the
Preferred Stock by the holders of Depository Receipts or redemption or
conversion of the Preferred Stock, except for taxes (including transfer taxes,
if any) and other governmental charges and such other charges as are expressly
provided in the Deposit Agreement to be at the expense of holders of Depository
Receipts or persons depositing Preferred Stock.
 
MISCELLANEOUS
 
    The Preferred Stock Depository will make available for inspection by holders
of Depository Receipts at its corporate office and its New York office, all
reports and communications from the Company which are delivered to the Preferred
Stock Depository as the holder of Preferred Stock.
 
    Neither the Preferred Stock Depository nor the Company will be liable if it
is prevented or delayed by law or any circumstance beyond its control in
performing its obligations under the Deposit Agreement. The obligations of the
Preferred Stock Depository under the Deposit Agreement are limited to performing
its duties thereunder without negligence or bad faith. The obligations of the
Company under the Deposit Agreement are limited to performing its duties
thereunder in good faith. Neither the Company nor the Preferred Stock Depository
is obligated to prosecute or defend any legal proceeding in respect of any
Depository Shares or Preferred Stock unless satisfactory indemnity is furnished.
The Company and the Preferred Stock Depository are entitled to rely upon advice
of or information from counsel, accountants or other persons believed to be
competent and on documents believed to be genuine.
 
    The Preferred Stock Depository may resign at any time or be removed by the
Company, effective upon the acceptance by its successor of its appointment;
provided, that if a successor Preferred Stock Depository has not been appointed
or accepted such appointment within 45 days after the Preferred Stock Depository
has delivered a notice of election to resign to the Company, the Preferred Stock
Depository may terminate the Deposit Agreement. See "--Amendment and Termination
of the Deposit Agreement" above.
 
                                       22

                        DESCRIPTION OF THE COMMON STOCK
 
    The following description is a summary of certain provisions of the Common
Stock and does not purport to be complete and is subject to, and is qualified in
its entirety by reference to, the Company's Bylaws and Articles and the laws of
the State of Idaho. The Prospectus Supplement relating to any offering of Common
Stock will describe terms relevant thereto including, without limitation, the
number of shares offered, the initial offering price and market price and
dividend information.
 
GENERAL
 
    Pursuant to the Company's Articles, the Company is authorized to issue up to
120,000,000 shares of Common Stock, without par value. As of October 1, 1998,
37,612,351 shares of Common Stock were issued and outstanding. All shares of
Common Stock currently outstanding are, and shares of Common Stock to be issued
in connection with any offering will be, fully paid and nonassessable. Each
share of Common Stock currently has attached to it one Right issued pursuant to
a Rights Agreement (each as defined below), as described below under "Certain
Matters That May Have an Anti-Takeover Effect--Rights Plan."
 
VOTING RIGHTS
 
    The holders of Common Stock are entitled to one vote per share on all
matters to be voted on by stockholders. Holders of Common Stock are not entitled
to cumulate their votes in the election of directors.
 
DIVIDENDS
 
    Holders of Common Stock will share ratably in dividends when, as and if
declared by the Board of Directors out of any tangible or intangible property
legally available therefor, subject to the rights of holders of any outstanding
shares of Preferred Stock.
 
OTHER RIGHTS
 
    On dissolution, liquidation or winding up of the Company, after payment in
full of the amounts required to be paid to holders of Preferred Stock, all
holders of Common Stock will be entitled to share ratably in any net assets
available for distribution to holders of shares of Common Stock.
 
    No shares of Common Stock are subject to redemption or have preemptive
rights to purchase additional shares of Common Stock. Common Stock does not have
any conversion or sinking fund provisions.
 
TRANSFER AGENTS AND REGISTRARS
 
    IDACORP and The Bank of New York will serve as both transfer agent and
registrar for the Common Stock.
 
             CERTAIN MATTERS THAT MAY HAVE AN ANTI-TAKEOVER EFFECT
 
   
PROVISIONS OF THE COMPANY'S ARTICLES OF INCORPORATION, AS AMENDED, AND AMENDED
  BYLAWS
    
 
    Certain provisions of the Company's Articles and Bylaws summarized below may
be deemed to have an anti-takeover effect and may delay, deter or prevent a
tender offer or takeover attempt that a holder of Common Stock might consider to
be in its best interest, including attempts that might result in a premium being
paid over the market price for shares held by holders of Common Stock.
 
    The Company's Articles and Bylaws provide that the number of directors of
the Company will not be more than 15 nor less than 9, with the exact number of
directors of the Company to be fixed from time to
 
                                       23

time, as provided in the Bylaws, by the affirmative vote of a majority of the
directors. The Articles provide that a director may be removed by the
shareholders only for cause at a meeting called for the purpose of removing him
by the affirmative vote of not less than two-thirds of the outstanding shares
entitled to vote in elections of directors. In addition, the Articles provide
that any vacancies will be filled by the affirmative vote of two-thirds of the
remaining members of the Board of Directors or by a sole remaining director,
though less than a quorum. As of the date of this Prospectus, the Board of
Directors has set the number of directors at 12. The Company's Articles also
provide for the division of the Board into three classes, which shall be as
nearly equal in number as possible, with directors in each class being elected
for a three-year term.
 
    The Company's Articles also provide that the affirmative vote of the holders
of at least 80% of the voting power of all classes of outstanding capital stock
entitled to vote in elections of directors, voting together as a single class,
is required to amend, repeal or adopt any provision inconsistent with the
provisions of the Articles discussed above, unless such action is recommended to
the shareholders by affirmative vote of two-thirds of the Continuing Directors
(as defined therein).
 
    The Company's Bylaws provide for an advance notice procedure for the
nomination, other than by or at the direction of the Board of Directors, of
candidates for election as directors as well as for other shareholder proposals
to be considered at annual meetings of shareholders. In general, notice of
intent to nominate a director or raise matters at such meetings will have to be
received in writing by the Company not less than 60 or more than 90 days prior
to the anniversary of the previous year's annual meeting of shareholders, and
must contain certain information concerning the person to be nominated or the
matters to be brought before the meeting and concerning the shareholder
submitting the proposal. Such advance notice requirements may delay the ability
of individuals to bring before shareholder meetings matters other than those
that the Company deems desirable and may provide sufficient time for the Company
to institute litigation or take other appropriate steps to respond to such
business, or to prevent such business from being acted upon, if such response or
prevention is thought to be necessary or desirable for any reason. The Company's
Articles and Bylaws also provide that special meetings of shareholders may be
called only by certain specified officers of the Company or by a majority of the
Board of Directors; special meetings of shareholders can also be called by
holders of not less than 20% of the shares entitled to vote. In addition, the
Company's Articles provide that any action required or permitted to be taken by
shareholders may be effected at a duly called annual or special meeting of
shareholders or may be effected by a written consent by the holders of all the
outstanding shares entitled to vote on the matter.
 
    The Articles and Bylaws further provide that the Bylaws may be altered,
amended or repealed by the affirmative vote of a majority of the directors (if
effected by action of the Board of Directors) or by the affirmative vote of the
holders of a majority of the total voting power of all shares entitled to vote
thereon (with certain exceptions relating to shareholder votes and the Board of
Directors, which require the affirmative vote of two-thirds of all shares
entitled to vote thereon).
 
    The Company's Articles do not provide for cumulative voting.
 
    The Company's Articles authorize the issuance of 20,000,000 shares of
Company Preferred Stock. The Board of Directors has the full authority to
determine the terms of any series of the Company's Preferred Stock. Although the
Company's Board of Directors currently has no intention of doing so, shares of
Company Preferred Stock could be issued in a manner (E.G., with disproportionate
or class voting rights) that could have the effect of discouraging takeover
attempts. The Board of Directors has reserved 1,200,000 shares of Company
Preferred Stock for issuance under the Rights Plan discussed below.
 
RIGHTS PLAN
 
    On September 10, 1998, the Board of Directors of the Company adopted a
Shareholder Rights Plan (the "Rights Plan"). The Company declared a dividend of
one Preferred Share Purchase Right (a "Right") for each outstanding share of
IDACORP Common Stock held at the close of business on October 1, 1998,
 
                                       24

or issued thereafter until the earlier of the date on which the Rights expire,
are redeemed or become exercisable. The Rights are currently not exercisable or
transferable apart from the Common Stock and will be exercisable only if a
person or group either becomes the beneficial owner of 20% or more of the
Company's outstanding voting stock (an "Acquiring Person") or commences or
announces an intention to make a tender or exchange offer that would result in
the beneficial ownership of 20% or more of the Company's voting stock. The
Company may redeem the Rights (but not less than all the Rights) at a price of
$0.01 per Right any time prior to the close of business on the tenth business
day after a person has become an Acquiring Person. Following the acquisition by
a person of a 20% position, each Right will entitle its holder (other than the
Acquiring Person, whose Rights are void), subject to any applicable regulatory
approval, to purchase for $95 the number of shares of IDACORP Common Stock, or
at the election of IDACORP, IDACORP Preferred Stock, having a market value of
$190. If the Company is acquired in a merger or other business combination, 50%
or more of its consolidated assets or earning power are sold or the Acquiring
Person engages in certain acts of self-dealing, each Right will entitle its
holder (other than the Acquiring Person, whose Rights are void), subject to any
applicable regulatory approval, to purchase for $95 the number of shares of the
acquiring company's common stock having a market value of $190. Any Rights that
are or were held by an Acquiring Person become void if any of these events
occurs. At any time after a person becomes an Acquiring Person, and prior to the
acquisition by the Acquiring Person of 50% or more of the Company's Common
Stock, the Company may exchange the Rights for one share of Company Common Stock
per Right, or cash or other assets of the Company having the same market value
as a share of Company Common Stock. The Rights expire on September 10, 2008.
 
CERTAIN IDAHO STATUTORY PROVISIONS
 
    The Company is subject to the Idaho Control Share Acquisition Law (the
"CSAL"), which is designed to protect minority shareholders in the event that a
person acquires or proposes to acquire, directly or indirectly, by tender offer
or otherwise, shares giving it at least 20%, at least 33 1/3%, or more than 50%
of the voting power in the election of directors (such an acquisition, a
"Control Share Acquisition"). The CSAL is applicable to a publicly-held Idaho
corporation which has at least 50 shareholders, such as the Company, unless a
provision in its articles of incorporation or bylaws, adopted in accordance with
the CSAL, makes an express election not to be subject to the CSAL. There are no
such provisions in the Company's Articles or Bylaws.
 
    Under the CSAL, an acquiring person is required to deliver to the
corporation an information statement disclosing, among other things, the
identity of the person, the terms of the acquisition or proposed acquisition and
the financing thereof. An acquiring person will not be able to vote those shares
acquired in a Control Share Acquisition that exceed one of the cited thresholds
(such shares, "Control Shares") unless a resolution approved by 66 2/3% of the
voting power of all shares entitled to vote thereon (excluding shares with
respect to which voting power can be exercised by the acquiring person or an
officer or director of the corporation) approves of such voting power. At the
request of the acquiring person, such a resolution must be put forth before
shareholders at a special meeting held within 55 days after receipt of the
information statement, provided that the acquiring person undertakes to pay the
costs of such special meeting and has delivered to the corporation copies of
definitive financing agreements with responsible entities for any required
financing of the Control Share Acquisition. If an information statement has not
been delivered to the corporation by the 10th day after a Control Share
Acquisition, or the shareholders of the corporation have voted not to accord
voting rights to the Control Shares, the corporation may redeem all (but not
less than all) of the Control Shares at their fair market value. Shares that are
not accorded voting rights pursuant to the CSAL regain their voting rights when
acquired by another person in an acquisition that is not subject to the CSAL.
 
    The Company also is subject to the Idaho Business Combination Law (the
"BCL"), which prohibits a corporation from engaging in certain business
combinations with an "interested shareholder" for a period of three years after
the date of the transaction in which the person became an interested
shareholder,
 
                                       25

unless, among other things, (i) the corporation's articles of incorporation or
bylaws include a provision that was adopted in accordance with the BCL and that
expressly provides that the corporation is not subject to the statute (the
Company has not made such an election), or (ii) a committee of the corporation's
Board of Directors approves of the business combination or the acquisition of
the shares before the date such shares were acquired. After the three year
moratorium period, the corporation may not consummate a business combination
unless, among other things, it is approved by the affirmative vote of the
holders of at least two-thirds of the outstanding shares entitled to vote (other
than those beneficially owned by the interested shareholder or an affiliate or
associate thereof) or the business combination meets certain minimum price and
form of payment requirements. An interested shareholder is defined to include,
with certain exceptions, any person who is the beneficial owner of 10% or more
of the voting power of the outstanding voting shares of the corporation.
Business combinations subject to the BCL include certain mergers,
consolidations, recapitalizations and reverse share splits.
 
    The application of the CSAL and the BCL may have the effect of delaying,
deferring or preventing a change of control of the Company.
 
                      DESCRIPTION OF PREFERRED SECURITIES
 
    The following description sets forth certain general terms and provisions of
the Preferred Securities to which any Prospectus Supplement may relate. The
particular terms of the Preferred Securities offered by any Prospectus
Supplement and the extent, if any, to which such general provisions may apply to
the Preferred Securities so offered will be described in the Prospectus
Supplement relating to such Preferred Securities. The Prospectus Supplement will
also set forth with respect to the particular Preferred Securities offered, the
specific designation, number of securities, liquidation amount per security, any
listing on a securities exchange, distribution rate (or method of calculation
thereof), dates on which distributions shall be payable and dates from which
distributions shall accrue, voting rights, if any, terms for any conversion or
exchange into other securities, any redemption or sinking fund provisions, any
other rights, preferences, privileges, limitations or restrictions relating to
the Preferred Securities and the terms upon which the proceeds of the sale of
the Preferred Securities shall be used to purchase a specific series of
Corresponding Subordinated Debt Securities of the Company.
 
    Pursuant to the terms of the Trust Agreement for each IDACORP Trust, each
Administrative Trustee, on behalf of such IDACORP Trust, is authorized to issue
the Preferred Securities and the Common Securities. The Preferred Securities of
a particular issue will represent preferred beneficial ownership interests in
the assets of such IDACORP Trust, and the holders thereof will be entitled to a
preference in certain circumstances with respect to Distributions and amounts
payable on redemption or liquidation over the Common Securities of such IDACORP
Trust, as well as other benefits as described in the corresponding Trust
Agreement. This summary of certain provisions of the Preferred Securities and
each Trust Agreement, which together with the applicable Prospectus Supplement
will describe the material terms thereof, does not purport to be complete and is
subject to, and is qualified in its entirety by reference to, all the provisions
of each Trust Agreement, including the definitions therein of certain terms, and
the Trust Indenture Act to each of which reference is hereby made. Wherever
particular defined terms of a Trust Agreement (as amended or supplemented from
time to time) are referred to herein or in a Prospectus Supplement, such defined
terms are incorporated herein or therein by reference. The form of the Trust
Agreement has been filed as an exhibit to the Registration Statement of which
this Prospectus forms a part. Each of the IDACORP Trusts is a legally separate
entity and the assets of one are not available to satisfy the obligations of any
of the others.
 
GENERAL
 
    The Preferred Securities of an IDACORP Trust will rank PARI PASSU, and
payments will be made thereon PRO RATA, with the Common Securities of that
IDACORP Trust except as described under "--Subordination of Common Securities."
Legal title to the Corresponding Subordinated Debt Securities
 
                                       26

will be held in the name of the relevant IDACORP Trust in trust for the benefit
of the holders of the related Preferred Securities and Common Securities. Each
Guarantee Agreement executed by the Company for the benefit of the holders of an
IDACORP Trust's Preferred Securities (each, a "Guarantee") will be a guarantee
on a subordinated basis with respect to the related Preferred Securities but
will not guarantee payment of Distributions or amounts payable on redemption or
liquidation of such Preferred Securities when the related IDACORP Trust does not
have funds on hand available to make such payments. See "Description of
Guarantees."
 
DISTRIBUTIONS
 
    Distributions on the Preferred Securities will be cumulative and will
accumulate whether or not there are funds of the applicable IDACORP Trust for
the payment of Distributions. Distributions will accrue from and will be payable
on such dates as are specified in the applicable Prospectus Supplement. Except
as specified in the applicable Prospectus Supplement, in the event that any date
on which Distributions are payable on the Preferred Securities is not a Business
Day (as defined below), payment of the Distribution payable on such date will be
made on the next succeeding day that is a Business Day (and without any interest
or other payment in respect to any such delay), except that, if such next
succeeding Business Day is in the next succeeding calendar year, payment of such
Distribution shall be made on the immediately preceding Business Day, in each
case with the same force and effect as if made on such date (each date on which
Distributions are payable in accordance with the foregoing, a "Distribution
Date"). Except as specified in the applicable Prospectus Supplement, a "Business
Day" shall mean any day other than a Saturday or a Sunday, or a day on which
banking institutions in The City of New York are authorized or required by law
to remain closed or a day on which the corporate trust office of the Property
Trustee or the Indenture Trustee under the Subordinated Indenture is closed for
business.
 
    Distributions on each Preferred Security will be payable at a rate specified
in the Prospectus Supplement for such Preferred Securities. The amount of
Distributions payable will be computed on the basis of a 360-day year of twelve
30-day months and the actual days elapsed in a partial month in a period unless
otherwise specified in the applicable Prospectus Supplement. Distributions to
which holders of Preferred Securities are entitled will accumulate additional
Distributions at the rate per annum if and as specified in the applicable
Prospectus Supplement. The term "Distributions" as used herein includes any such
additional Distributions unless otherwise stated.
 
    If provided in the applicable Prospectus Supplement, the Company shall have
the right at any time and from time to time during the term of any series of
Corresponding Subordinated Debt Securities to defer payment of interest for such
number of consecutive interest payment periods as may be specified in the
applicable Prospectus Supplement (each, an "Extension Period"), subject to the
terms, conditions and covenants, if any, specified in such Prospectus
Supplement, provided that such Extension Period may not extend beyond the
maturity date of such series of Corresponding Subordinated Debt Securities.
Certain United States Federal income tax consequences and special considerations
applicable to any such Corresponding Subordinated Debt Securities will be
described in the applicable Prospectus Supplement. As a consequence of any such
extension, during any such Extension Period, Distributions on the corresponding
Preferred Securities would also be deferred by the applicable IDACORP Trust.
During any such Extension Period, quarterly Distributions will continue to
accumulate, compounded on a quarterly basis, to the extent permitted by
applicable law.
 
    If the Company shall have given notice of its election of an Extension
Period with respect to the Corresponding Subordinated Debt Securities of a
series and shall not have rescinded such notice, or such Extension Period, or
any extension thereof, shall be continuing, the Company may not make certain
payments. See "Description of the Debt Securities--Certain Provisions Relating
to Corresponding Subordinated Debt Securities--Restrictions on Certain Payments"
for a summary of such restrictions and the additional circumstances in which the
Company is restricted from making such payments.
 
                                       27

    The revenue of each IDACORP Trust available for distribution to holders of
its Preferred Securities will be limited to payments under the Corresponding
Subordinated Debt Securities in which the IDACORP Trust will invest the proceeds
from the issuance and sale of its Trust Securities. See "Description of the Debt
Securities--Certain Provisions Relating to Corresponding Subordinated Debt
Securities." If the Company does not make interest payments on such
Corresponding Subordinated Debt Securities, the Property Trustee will not have
funds available to pay Distributions on the related Preferred Securities. The
payment of Distributions (if and to the extent the IDACORP Trust has funds
legally available for the payment of such Distributions and cash sufficient to
make such payments) is guaranteed by the Company on a limited basis as set forth
herein under "Description of Guarantees."
 
    Distributions on the Preferred Securities will be payable to the holders
thereof as they appear on the register of such IDACORP Trust on the relevant
record dates, which, as long as the Preferred Securities remain in book-entry
form, will be one Business Day prior to the relevant Distribution Date. Unless
otherwise specified in the applicable Prospectus Supplement, and subject to any
applicable laws and regulations and the provisions of the applicable Trust
Agreement, each such payment will be made as described under "Book-Entry
Issuance." In the event any Preferred Securities are not in book-entry form, the
relevant record date for such Preferred Securities shall be the date 15 days
prior to the relevant Distribution Date.
 
PAYMENT OF EXPENSES
 
    Pursuant to the Subordinated Indenture, the Company, as borrower, has agreed
to pay all debts and obligations (other than with respect to the Trust
Securities) and all costs and expenses of the applicable IDACORP Trust
(including, but not limited to, all costs and expenses relating to the
organization of the applicable IDACORP Trust, the fees and expenses of the
Property Trustee, the Delaware Trustee and the Administrative Trustees and all
costs and expenses relating to the operation of the applicable IDACORP Trust
(other than with respect to the Trust Securities)) and to pay any and all taxes,
duties, assessments or other governmental charges of whatever nature (other than
United States withholding taxes) imposed by the United States or any other
taxing authority, so that the net amounts received and retained by the
applicable IDACORP Trust after paying such fees, expenses, debts and obligations
will be equal to the amounts the applicable IDACORP Trust would have received
and retained had no such fees, expenses, debts and obligations been incurred by
or imposed on the applicable IDACORP Trust. The foregoing obligations of the
Company are for the benefit of, and shall be enforceable by, any person to whom
such fees, expenses, debts and obligations are owed (each a "Creditor"), whether
or not such Creditor has received notice thereof. Any such Creditor may enforce
such obligations of the Company directly against the Company, and the Company
has agreed to irrevocably waive any right or remedy to require that any such
Creditor take any action against the applicable IDACORP Trust or any other
person before proceeding against the Company. The Company shall execute such
additional agreements as may be necessary to give full effect to the foregoing.
(Section 4.7 of the Subordinated Indenture)
 
                                       28

REDEMPTION OR EXCHANGE
 
    Upon the repayment or redemption, in whole or in part, of any Corresponding
Subordinated Debt Securities, whether at maturity or upon earlier redemption,
the proceeds from such repayment or redemption shall be applied by the Property
Trustee to redeem a Like Amount (as defined below) of the Trust Securities, upon
not less than 30 nor more than 60 days notice, at a redemption price (the
"Redemption Price") equal to the aggregate Liquidation Amount of such Trust
Securities plus accumulated but unpaid Distributions thereon to the date fixed
for redemption (the "Redemption Date") and the related amount of the premium, if
any, paid by the Company upon the concurrent redemption of such Corresponding
Subordinated Debt Securities. See "Description of the Debt Securities--Certain
Provisions Relating to Corresponding Subordinated Debt Securities--Redemption."
If fewer than all of any series of Corresponding Subordinated Debt Securities
are to be repaid or redeemed on a Redemption Date, then the proceeds from such
repayment or redemption shall be allocated to the redemption PRO RATA (based on
Liquidation Amounts) of the related Common Securities and Preferred Securities.
The particular Preferred Securities to be redeemed shall be selected by the
Property Trustee from outstanding Preferred Securities not previously called for
redemption, by such means as the Property Trustee shall deem fair and
appropriate.
 
    The Company will have the right to redeem any series of Corresponding
Subordinated Debt Securities on such terms as may be specified in the applicable
Prospectus Supplement.
 
    "Like Amount" means (i) with respect to a redemption of any series of Trust
Securities, Trust Securities of such series having a Liquidation Amount (as
defined below) equal to the principal amount of Corresponding Subordinated Debt
Securities to be contemporaneously redeemed in accordance with the Subordinated
Indenture, allocated to the Common Securities and the Preferred Securities based
upon the relative Liquidation Amounts of such classes and the proceeds of which
will be used to pay the Redemption Price of such Trust Securities, and (ii) with
respect to a distribution of Corresponding Subordinated Debt Securities to
holders of any series of Trust Securities in connection with a dissolution or
liquidation of the related IDACORP Trust, Corresponding Subordinated Debt
Securities having a principal amount equal to the Liquidation Amount of the
Trust Securities of the holder to whom such Corresponding Subordinated Debt
Securities are distributed. "Liquidation Amount" means the stated amount per
Trust Security specified in the applicable Prospectus Supplement.
 
REDEMPTION AND EXCHANGE PROCEDURES
 
    Preferred Securities redeemed on each Redemption Date shall be redeemed at
the Redemption Price with the applicable proceeds from the contemporaneous
redemption of the Corresponding Subordinated Debt Securities. Redemptions of the
Preferred Securities shall be made and the Redemption Price shall be payable on
each Redemption Date only to the extent that the related IDACORP Trust has funds
on hand available for the payment of such Redemption Price. See "--Subordination
of Common Securities."
 
    If an IDACORP Trust gives a notice of redemption in respect of its Preferred
Securities, then, by 12:00 noon, New York City time, on the Redemption Date, to
the extent funds are available, the Property Trustee will deposit irrevocably
with DTC funds sufficient to pay the applicable Redemption Price and will give
DTC irrevocable instructions and authority to pay the Redemption Price to the
holders of such Preferred Securities. See "Book-Entry Issuance." If such
Preferred Securities are no longer in book-entry form, the Property Trustee, to
the extent funds are available, will irrevocably deposit with the paying agent
for such Preferred Securities funds sufficient to pay the applicable Redemption
Price and will give such paying agent irrevocable instructions and authority to
pay the Redemption Price to the holders thereof upon surrender of their
certificates evidencing such Preferred Securities. Notwithstanding the
foregoing, Distributions payable on or prior to the Redemption Date for any
Preferred Securities called for redemption shall be payable to the holders of
such Preferred Securities on the relevant record dates for the related
Distribution Dates. If notice of redemption shall have been given and funds
deposited as required,
 
                                       29

then immediately prior to the close of business (New York City time) on the date
of such deposit, all rights of the holders of such Preferred Securities so
called for redemption will cease, except the right of the holders of such
Preferred Securities to receive the Redemption Price and any unpaid Distribution
payable on or prior to the Redemption Date, in each case without interest, and
such Preferred Securities will cease to be outstanding. Except as specified in
the applicable Prospectus Supplement, in the event that any Redemption Date is
not a Business Day, then payment of the Redemption Price payable on such date
will be made on the next succeeding day which is a Business Day except that, if
such succeeding Business Day falls in the next calendar year, such payment will
be paid on the immediately preceding Business Day, in each case, with the same
force and effect as if made on such date. In the event that payment of the
Redemption Price in respect of Preferred Securities called for redemption is
improperly withheld or refused and not paid either by the IDACORP Trust or by
the Company pursuant to the Guarantee as described under "Description of
Guarantees," Distributions on such Preferred Securities will continue to accrue
at the then applicable rate, from the Redemption Date originally established by
the IDACORP Trust for such Preferred Securities to the date such Redemption
Price is actually deposited with DTC or the paying agent, as applicable, in
which case such date will be the date fixed for redemption for purposes of
calculating the Redemption Price; provided that if the Redemption Price is not
deposited by 12:00 noon on such date, the next succeeding Business Day shall be
the date fixed for redemption for purposes of calculating the Redemption Price.
 
    Subject to applicable law (including, without limitation, United States
Federal securities law), the Company or its subsidiaries may at any time and
from time to time purchase outstanding Preferred Securities by tender, in the
open market or by private agreement.
 
    Payment of the Redemption Price on the Preferred Securities and any
distribution of Corresponding Subordinated Debt Securities to holders of
Preferred Securities shall be made to the applicable recordholders thereof as
they appear on the register for such Preferred Securities on the relevant record
date, which shall be one Business Day prior to the relevant Redemption Date or
liquidation date, as applicable; provided, however, that in the event that any
Preferred Securities are not in book-entry form, the relevant record date for
such Preferred Securities shall be a date at least 15 days prior to the
Redemption Date or liquidation date, as applicable, as specified in the
applicable Prospectus Supplement.
 
    If fewer than all of the Preferred Securities and Common Securities issued
by an IDACORP Trust are to be redeemed on a Redemption Date, then the aggregate
Liquidation Amount of such Preferred Securities and Common Securities to be
redeemed shall be allocated PRO RATA to the Preferred Securities and the Common
Securities based upon the relative Liquidation Amounts of such classes. The
particular Preferred Securities to be redeemed shall be selected not more than
60 days prior to the Redemption Date by the Property Trustee from the
outstanding Preferred Securities not previously called for redemption, by such
method as the Property Trustee shall deem fair and appropriate and which may
provide for the selection for redemption of portions (equal to the Liquidation
Amount or an integral multiple of the Liquidation Amount in excess thereof) of
the aggregate Liquidation Amount of Preferred Securities of a denomination
larger than the Liquidation Amount. The Property Trustee shall promptly notify
the trust registrar in writing of the Preferred Securities selected for
redemption and, in the case of any Preferred Securities selected for partial
redemption, the Liquidation Amount thereof to be redeemed. For all purposes of
each Trust Agreement, unless the context otherwise requires, all provisions
relating to the redemption of Preferred Securities shall relate, in the case of
any Preferred Securities redeemed or to be redeemed only in part, to the portion
of the aggregate Liquidation Amount of Preferred Securities which has been or is
to be redeemed.
 
SUBORDINATION OF COMMON SECURITIES
 
    Payment of Distributions on, and the Redemption Price of, each IDACORP
Trust's Preferred Securities and Common Securities, as applicable, shall be made
PRO RATA based on the Liquidation Amount of such Preferred Securities and Common
Securities; provided, however, that if on any Distribution Date
 
                                       30

or Redemption Date an Event of Default with respect to any Subordinated Debt
Security shall have occurred and be continuing, no payment of any Distribution
on, or Redemption Price of, any of such IDACORP Trust's Common Securities, and
no other payment on account of the redemption, liquidation or other acquisition
of such Common Securities, shall be made unless payment in full in cash of all
accumulated and unpaid Distributions on all of the IDACORP Trust's outstanding
Preferred Securities for all Distribution periods terminating on or prior
thereto, or in the case of payment of the Redemption Price the full amount of
such Redemption Price on all of the IDACORP Trust's outstanding Preferred
Securities then called for redemption, shall have been made or provided for, and
all funds available to the Property Trustee shall first be applied to the
payment in full in cash of all Distributions on, or Redemption Price of, the
IDACORP Trust's Preferred Securities then due and payable.
 
    In the case of any Event of Default with respect to any Subordinated Debt
Security, the Company as holder of such IDACORP Trust's Common Securities will
be deemed to have waived any right to act with respect to any such Event of
Default under the applicable Trust Agreement until the effect of all such Events
of Default with respect to such Preferred Securities has been cured, waived or
otherwise eliminated. Until any such Events of Default under the applicable
Trust Agreement with respect to the Preferred Securities have been so cured,
waived or otherwise eliminated, the Property Trustee shall act solely on behalf
of the holders of such Preferred Securities and not on behalf of the Company as
holder of the IDACORP Trust's Common Securities, and only the holders of such
Preferred Securities will have the right to direct the Property Trustee to act
on their behalf.
 
LIQUIDATION DISTRIBUTION UPON DISSOLUTION
 
    Unless otherwise specified in the applicable Prospectus Supplement, the
Company has the right at any time to terminate any IDACORP Trust and, after
satisfaction of the liabilities of creditors of such IDACORP Trust as provided
by applicable law, cause such Corresponding Subordinated Debt Securities in
respect of the Preferred Securities and Common Securities issued by such IDACORP
Trust to be distributed to the holders of such Preferred Securities and Common
Securities in liquidation of the IDACORP Trust.
 
   
    Pursuant to each Trust Agreement, each IDACORP Trust shall automatically
dissolve upon expiration of its term and shall dissolve on the first to occur
of: (i) certain events of bankruptcy, dissolution or liquidation of the Company;
(ii) the distribution of a Like Amount of the Corresponding Subordinated Debt
Securities to the holders of its Trust Securities, if the Company, as Sponsor,
has given written direction to the Property Trustee to dissolve such IDACORP
Trust (which direction is optional and wholly within the discretion of the
Company, as Sponsor); (iii) redemption of all of the IDACORP Trust's Preferred
Securities as described under "--Redemption or Exchange"; and (iv) the entry of
an order for the dissolution of such IDACORP Trust by a court of competent
jurisdiction.
    
 
    If an early dissolution occurs as described in clause (i), (ii) or (iv)
above, the IDACORP Trust shall be liquidated by the Issuer Trustees as
expeditiously as the Issuer Trustees determine to be possible by distributing,
after satisfaction of liabilities to creditors of such IDACORP Trust as provided
by applicable law, to the holders of such Trust Securities a Like Amount of the
Corresponding Subordinated Debt Securities, unless such distribution is
determined by the Property Trustee not to be practical, in which event such
holders will be entitled to receive out of the assets of the IDACORP Trust
available for distribution to holders, after satisfaction of liabilities to
creditors of such IDACORP Trust as provided by applicable law, an amount equal
to, in the case of holders of Preferred Securities, the aggregate of the
Liquidation Amount plus accrued and unpaid Distributions thereon to the date of
payment (such amount being the "Liquidation Distribution"). If such Liquidation
Distribution can be paid only in part because such IDACORP Trust has
insufficient assets available to pay in full the aggregate Liquidation
Distribution, then the amounts payable directly by such IDACORP Trust on its
Preferred Securities shall be paid on a PRO RATA basis. The holder of such
IDACORP Trust's Common Securities will be entitled to receive distributions upon
any such liquidation PRO RATA with the holders of its Preferred Securities,
except that if a Subordinated
 
                                       31

Debt Security Event of Default has occurred and is continuing, the Preferred
Securities shall have a priority over the Common Securities. A supplement to the
Subordinated Indenture may provide that if an early dissolution occurs as
described in clause (iv) above, the Corresponding Subordinated Debt Securities
may be subject to optional redemption in whole (but not in part).
 
    After the date fixed for any distribution of Corresponding Subordinated Debt
Securities for any series of Preferred Securities (i) such series of Preferred
Securities will no longer be deemed to be outstanding, (ii) certificates
representing the Corresponding Subordinated Debt Securities to be delivered upon
such distribution will be issued to the holders of the certificates for the
Trust Securities upon surrender of such certificates for exchange, (iii) the
company shall use its reasonable efforts to have the Subordinated Debt
Securities listed on the exchange, interdealer quotation system or
self-regulatory system as the Preferred Securities are then listed. and (iv) any
certificates representing such series of Preferred Securities not so exchanged
will be deemed to represent the Corresponding Subordinated Debt Securities
having a principal amount equal to the stated liquidation amount of such series
of Preferred Securities, and accruing interest at the rate provided for in the
Debt Securities until such certificates are presented to the Administrative
Trustees or their agent for transfer or reissuance.
 
    There can be no assurance as to the market prices for the Preferred
Securities or the Corresponding Subordinated Debt Securities that may be
distributed in exchange for Preferred Securities if a dissolution and
liquidation of an IDACORP Trust were to occur. Accordingly, the Preferred
Securities that an investor may purchase, or the Corresponding Subordinated Debt
Securities that an investor may receive on dissolution and liquidation of an
IDACORP Trust, may trade at a discount to the price that the investor paid to
purchase the Preferred Securities.
 
EVENT OF DEFAULT; NOTICE
 
    Unless otherwise specified in the applicable Prospectus Supplement, the
following event constitutes an "Event of Default" under each Trust Agreement (a
"Trust Event of Default") with respect to the Preferred Securities issued
thereunder (whatever the reason for such Trust Event of Default and whether it
shall be voluntary or involuntary or be effected by operation of law or pursuant
to any judgment, decree or order of any court or any order, rule or regulation
of any administrative or governmental body): the occurrence of an Event of
Default with respect to a Corresponding Subordinated Debt Security under the
Subordinated Indenture (see "Description of the Debt Securities--Events of
Default").
 
   
    Within 90 days after the occurrence of a default actually known to the
Property Trustee, the Property Trustee shall transmit notice of such default to
the holders of such IDACORP Trust's Preferred Securities, the Administrative
Trustees and the Company, as Sponsor, unless such default shall have been cured
or waived before the giving of such notice (the term "default" or "defaults"
being defined to mean any event or condition which is, or with notice or lapse
of time or both would become, a Trust Event of Default); provided that, except
in the case of default in the payment of the principal of, or premium, if any,
or interest, if any, on, any of the Subordinated Debt Securities of such series,
the Property Trustee shall be protected in withholding such notice if and so
long as the board of directors, the executive committee or a trust committee of
directors or responsible officers of the Property Trustee in good faith
determines that the withholding of such notice is in the interests of the
Securityholders of such series. The Company, as Sponsor, and the Administrative
Trustees are required to file annually with the Property Trustee a certificate
as to whether or not they are in compliance with all the conditions and
covenants applicable to them under each Trust Agreement.
    
 
    If an Event of Default with respect to a Corresponding Subordinated Debt
Security has occurred and is continuing, the Preferred Securities shall have a
preference over the Common Securities upon termination of each IDACORP Trust as
described above. See "--Liquidation Distribution Upon Dissolution." The
existence of a Trust Event of Default does not entitle the holders of Preferred
Securities to accelerate the maturity thereof.
 
                                       32

REMOVAL OF ISSUER TRUSTEES
 
    Unless an Event of Default with respect to a Corresponding Subordinated Debt
Security shall have occurred and be continuing, any Issuer Trustee may be
removed at any time by the holder of the Common Securities. If a Trust Event of
Default resulting from an Event of Default with respect to a Corresponding
Subordinated Debt Security has occurred and is continuing, the Property Trustee
and the Delaware Trustee may be removed at such time by the holders of a
majority in Liquidation Amount of the outstanding Preferred Securities. In no
event will the holders of the Preferred Securities have the right to vote to
appoint, remove or replace the Administrative Trustees, which voting rights are
vested exclusively in the Company as the holder of the Common Securities. No
resignation or removal of an Issuer Trustee and no appointment of a successor
trustee shall be effective until the acceptance of appointment by the successor
trustee in accordance with the provisions of the applicable Trust Agreement.
 
CO-TRUSTEES AND SEPARATE PROPERTY TRUSTEE
 
    Unless a Trust Event of Default shall have occurred and be continuing, at
any time or times, for the purpose of meeting the legal requirements of the
Trust Indenture Act or of any jurisdiction in which any part of the Trust
Property may at the time be located, the Company, as the holder of the Common
Securities, and the Administrative Trustees shall have power to appoint one or
more persons either to act as a co-trustee, jointly with the Property Trustee,
of all or any part of such Trust Property, or to act as separate trustee of any
such property, in either case with such powers as may be provided in the
instrument of appointment, and to vest in such person or persons in such
capacity any property, title, right or power deemed necessary or desirable,
subject to the provisions of the applicable Trust Agreement. In case an Event of
Default with respect to a Subordinated Debt Security has occurred and is
continuing, the Property Trustee alone shall have power to make such
appointment.
 
MERGER OR CONSOLIDATION OF PROPERTY, DELAWARE TRUSTEES
 
    Any corporation into which the Property Trustee or the Delaware Trustee may
be merged or converted or with which it may be consolidated, or any corporation
resulting from any merger, conversion or consolidation to which such Trustee
shall be a party, or any corporation succeeding to all or substantially all the
corporate trust business of such Trustee, shall be the successor of such Trustee
under each Trust Agreement, provided such corporation shall be otherwise
qualified and eligible.
 
MERGERS, CONSOLIDATIONS, CONVERSIONS, AMALGAMATIONS OR REPLACEMENTS OF THE
  IDACORP TRUSTS
 
    An IDACORP Trust may not merge with or into, consolidate, convert into,
amalgamate, or be replaced by, or convey, transfer or lease its properties and
assets substantially as an entirety to any corporation or other Person, except
as described below, as described in "--Liquidation Distribution Upon
Dissolution" or as described in the Prospectus Supplement with respect to the
Preferred Securities. An IDACORP Trust may, at the request of the Company, with
the consent of the Administrative Trustees and without the consent of the
holders of the Preferred Securities, merge with or into, consolidate, convert
into, amalgamate, or be replaced by or convey, transfer or lease its properties
and assets substantially as an entirety to a trust organized as such under the
laws of any State; provided, that (i) such successor entity either (a) expressly
assumes all of the obligations of such IDACORP Trust with respect to the
Preferred Securities or (b) substitutes for the Preferred Securities other
securities having substantially the same terms as the Preferred Securities (the
"Successor Securities") so long as the Successor Securities rank the same as the
Preferred Securities rank in priority with respect to distributions and payments
upon liquidation, redemption and otherwise, (ii) the Company expressly appoints
a trustee of such successor entity possessing the same powers and duties as the
Property Trustee as the holder of the Corresponding Subordinated Debt
Securities, (iii) the Successor Securities are listed or traded, or any
Successor Securities will be listed upon notification of issuance, on any
national securities exchange or other organization on which the Preferred
Securities are then listed or traded, if any, (iv) such merger, consolidation,
conversion, amalgamation, replacement, conveyance, transfer or lease does not
cause the Preferred Securities (including any Successor Securities) to be
downgraded by any nationally recognized statistical rating organization,
 
                                       33

(v) such merger, consolidation, conversion, amalgamation, replacement,
conveyance, transfer or lease does not adversely affect the rights, preferences
and privileges of the holders of the Preferred Securities (including any
Successor Securities) in any material respect, (vi) such successor entity has a
purpose substantially similar to that of the IDACORP Trust, (vii) prior to such
merger, consolidation, conversion, amalgamation, replacement, conveyance,
transfer or lease, the Company has received an opinion of counsel to the effect
that (a) such merger, consolidation, conversion, amalgamation, replacement,
conveyance, transfer or lease does not adversely affect the rights, preferences
and privileges of the holders of the Preferred Securities (including any
Successor Securities) in any material respect, and (b) following such merger,
consolidation, conversion, amalgamation, replacement, conveyance, transfer or
lease, neither the IDACORP Trust nor such successor entity will be required to
register as an investment company under the Investment Company Act and (viii)
the Company or any permitted successor or assignee owns all of the common
securities of such successor entity and guarantees the obligations of such
successor entity under the Successor Securities at least to the extent provided
by the Guarantee. Notwithstanding the foregoing, an IDACORP Trust shall not,
except with the consent of holders of 100% in Liquidation Amount of the
Preferred Securities, merge with or into, consolidate, convert into, amalgamate,
or be replaced by or convey, transfer or lease its properties and assets
substantially as an entirety to any other person or permit any other entity to
consolidate, amalgamate, merge with or into, or replace it if such merger,
consolidation, conversion, amalgamation, replacement, conveyance, transfer or
lease would cause the IDACORP Trust or the successor entity to be classified as
other than a grantor trust for United States Federal income tax purposes.
 
VOTING RIGHTS; AMENDMENT OF EACH TRUST AGREEMENT
 
    Except as provided below and under "Description of Guarantees--Amendments
and Assignment" and as otherwise required by law and the applicable Trust
Agreement, the holders of the Preferred Securities will have no voting rights.
 
    Each Trust Agreement may be amended from time to time by the Company, the
Property Trustee and the Administrative Trustees, without the consent of the
holders of the Preferred Securities (i) to cure any ambiguity, correct or
supplement any provisions in such Trust Agreement that may be inconsistent with
any other provision, or to make any other provisions with respect to matters or
questions arising under such Trust Agreement, which shall not be inconsistent
with the other provisions of such Trust Agreement or (ii) to modify, eliminate
or add to any provisions of such Trust Agreement to such extent as shall be
necessary to ensure that the IDACORP Trust will be classified for United States
Federal income tax purposes as a grantor trust at all times that any Trust
Securities are outstanding or to ensure that the IDACORP Trust will not be
required to register as an "investment company" under the Investment Company
Act; provided, however, that in the case of clause (i), such action shall not
adversely affect in any material respect the interests of any holder of Trust
Securities, and any such amendments of such Trust Agreement shall become
effective when notice thereof is given to the holders of Trust Securities. Each
Trust Agreement may be amended by the Issuer Trustees and the Company with (i)
the consent of holders representing not less than a majority (based upon
Liquidation Amounts) of the outstanding Trust Securities and (ii) receipt by the
Issuer Trustees of an opinion of counsel to the effect that such amendment or
the exercise of any power granted to the Issuer Trustees in accordance with such
amendment will not affect the IDACORP Trust's status as a grantor trust for
United States Federal income tax purposes or the IDACORP Trust's exemption from
status as an "investment company" under the Investment Company Act; provided
that without the consent of each affected holder of Trust Securities, such Trust
Agreement may not be amended to (i) change the amount or timing of any
Distribution on the Trust Securities or otherwise adversely affect the amount of
any Distribution required to be made in respect of the Trust Securities as of a
specified date or (ii) restrict the right of a holder of Trust Securities to
institute suit for the enforcement of any such payment on or after such date.
 
    So long as any Corresponding Subordinated Debt Securities are held by the
Property Trustee, the Issuer Trustees shall not (i) direct the time, method and
place of conducting any proceeding for any remedy available to the Indenture
Trustee under the Subordinated Indenture, or executing any trust or power
conferred on the Indenture Trustee with respect to such Corresponding
Subordinated Debt
 
                                       34

Securities, (ii) waive any past default that is waivable under Section 6.1 of
the Subordinated Indenture, (iii) exercise any right to rescind or annul a
declaration that the principal of all the Corresponding Subordinated Debt
Securities shall be due and payable or (iv) consent to any amendment,
modification or termination of the Subordinated Indenture or such Corresponding
Subordinated Debt Securities, where such consent shall be required, without, in
each case, obtaining the prior approval of the holders of at least a majority in
aggregate Liquidation Amount of all outstanding Preferred Securities; provided,
however, that where a consent under the Subordinated Indenture would require the
consent of each holder of Corresponding Subordinated Debt Securities affected
thereby, no such consent shall be given by the Property Trustee without the
prior consent of each holder of the related Preferred Securities. The Issuer
Trustees shall not revoke any action previously authorized or approved by a vote
of the holders of the Preferred Securities except by subsequent vote of the
holders of the Preferred Securities. The Property Trustee shall notify all
holders of Preferred Securities of any notice of default received from the
Indenture Trustee with respect to the Corresponding Subordinated Debt
Securities. In addition to obtaining the foregoing approvals of the holders of
the Preferred Securities, prior to taking any of the foregoing actions, the
Issuer Trustees shall obtain an opinion of counsel experienced in such matters
to the effect that the IDACORP Trust will not be classified as an association
taxable as a corporation for United States Federal income tax purposes on
account of such action.
 
    Any required approval of holders of Preferred Securities may be given at a
meeting of holders of Preferred Securities convened for such purpose or pursuant
to written consent. The Property Trustee will cause a notice of any meeting at
which holders of Preferred Securities are entitled to vote to be given to each
holder of record of Preferred Securities in the manner set forth in each Trust
Agreement.
 
    No vote or consent of the holders of Preferred Securities will be required
for an IDACORP Trust to redeem and cancel its Preferred Securities in accordance
with the applicable Trust Agreement.
 
    Notwithstanding that holders of Preferred Securities are entitled to vote or
consent under any of the circumstances described above, any of the Preferred
Securities that are owned by the Company, the Issuer Trustees or any affiliate
of the Company or any Issuer Trustees, shall, for purposes of such vote or
consent, be treated as if they were not outstanding.
 
GLOBAL PREFERRED SECURITIES
 
    Unless otherwise provided in the Prospectus Supplement relating to an
offering of Preferred Securities and any Corresponding Subordinated Debt
Securities, the Preferred Securities and the Corresponding Subordinated Debt
Securities will be issued only as fully-registered Global Securities registered
in the name of the Depository identified in the applicable Prospectus
Supplement. One or more fully-registered Global Securities will be issued for
the Preferred Securities of each IDACORP Trust and the Corresponding
Subordinated Debt Securities, representing in the aggregate the total number of
such IDACORP Trust's Preferred Securities or aggregate principal balance of
Corresponding Subordinated Debt Securities, respectively, and will be deposited
with the Depository.
 
    For a description of such depository arrangements, see "Book-Entry
Issuance." Any additional or alternative terms of the depository arrangements
with respect to a series of Preferred Securities and any Corresponding
Subordinated Debt Securities and the rights of and limitations on owners of
beneficial interests in Book-Entry Securities (as defined herein) representing
all or a portion of a series of Preferred Securities and any Corresponding
Subordinated Debt Securities may be described in the Prospectus Supplement
relating to such series.
 
PAYMENT AND PAYING AGENCY
 
    Payments in respect of the Preferred Securities shall be made to the
Depository, which shall credit the relevant accounts at the Depository on the
applicable Distribution Dates or, if any IDACORP Trust's Preferred Securities
are not held by the Depository, such payments shall be made by check mailed to
the address of the holder entitled thereto as such address shall appear on the
Register. Unless otherwise specified in the applicable Prospectus Supplement,
the paying agent (the "Paying Agent") shall initially be
 
                                       35

the Property Trustee and any co-paying agent chosen by the Property Trustee and
acceptable to the Administrative Trustees and the Company. The Paying Agent
shall be permitted to resign as Paying Agent upon 30 days' written notice to the
Administrative Trustees, the Property Trustee and the Company. In the event that
the Property Trustee shall no longer be the Paying Agent, the Administrative
Trustees shall appoint a successor (which shall be a bank or trust company)
acceptable to the Property Trustee and the Company to act as Paying Agent.
 
REGISTRAR AND TRANSFER AGENT
 
    Unless otherwise specified in the applicable Prospectus Supplement, the
Property Trustee will act as registrar and transfer agent for the Preferred
Securities.
 
    Registration of transfers of Preferred Securities will be effected without
charge by or on behalf of each IDACORP Trust, but upon payment of any tax or
governmental charges that may be imposed in connection with any transfer or
exchange. The IDACORP Trusts will not be required to register or cause to be
registered the transfer of their Preferred Securities after such Preferred
Securities have been called for redemption.
 
INFORMATION CONCERNING THE PROPERTY TRUSTEE
 
    The Property Trustee, other than during the occurrence and continuance of a
Trust Event of Default, undertakes to perform only such duties as are
specifically set forth in each Trust Agreement and, after such Trust Event of
Default, must exercise the same degree of care and skill as a prudent person
would exercise or use in the conduct of his or her own affairs. Subject to this
provision, the Property Trustee is under no obligation to exercise any of the
rights or powers vested in it by the applicable Trust Agreement at the request
or direction of any holder of Preferred Securities unless it is offered
reasonable indemnity against the costs, expenses and liabilities that might be
incurred thereby. If in performing its duties under the Trust Agreement, the
Property Trustee is required to decide between alternative courses of action,
construe ambiguous provisions in the applicable Trust Agreement or is unsure of
the application of any provision of the applicable Trust Agreement, and the
matter is not one on which holders of Preferred Securities are entitled under
such Trust Agreement to vote, then the Property Trustee shall take such action
as is directed by the Company and if not so directed, shall take such action as
it deems advisable and in the best interests of the holders of the Trust
Securities and will have no liability except for its own bad faith, negligence
or willful misconduct.
 
    For information concerning the relationship between Bankers Trust, the
Property Trustee, and the Company, see "Description of the Debt
Securities--Concerning the Indenture Trustees."
 
MISCELLANEOUS
 
    The Administrative Trustees are authorized and directed to conduct the
affairs of and to operate the IDACORP Trusts so that no IDACORP Trust will be
deemed to be an "investment company" required to be registered under the
Investment Company Act or taxed as a corporation for United States Federal
income tax purposes and so that the Corresponding Subordinated Debt Securities
will be treated as indebtedness of the Company for United States Federal income
tax purposes. In this connection, the Company and the Administrative Trustees
are authorized to take any action, not inconsistent with applicable law, the
certificate of trust of each IDACORP Trust or each Trust Agreement, that each of
the Company and the Administrative Trustees determine in its discretion to be
necessary or desirable for such purposes, as long as such action does not
adversely affect in any material respect the interests of the holders of the
related Preferred Securities.
 
    Holders of the Preferred Securities have no preemptive or similar rights.
 
    No IDACORP Trust may borrow money or issue debt or mortgage or pledge any of
its assets.
 
                                       36

                           DESCRIPTION OF GUARANTEES
 
    A Guarantee will be executed and delivered by the Company concurrently with
the issuance by each IDACORP Trust of its Preferred Securities for the benefit
of the holders from time to time of such Preferred Securities. Unless otherwise
specified in the applicable Prospectus Supplement, Bankers Trust will act as
indenture trustee ("Guarantee Trustee") under each Guarantee for the purposes of
compliance with the Trust Indenture Act, and each Guarantee will be qualified as
an indenture under the Trust Indenture Act. This summary of certain provisions
of the Guarantees does not purport to be complete and is subject to, and
qualified in its entirety by reference to, all of the provisions of each
Guarantee Agreement, including the definitions therein of certain terms, and the
Trust Indenture Act. The form of the Guarantee has been filed as an exhibit to
the Registration Statement of which this Prospectus forms a part. Reference in
this summary to Preferred Securities means that IDACORP Trust's Preferred
Securities to which a Guarantee relates. The Guarantee Trustee will hold each
Guarantee for the benefit of the holders of the related IDACORP Trust's
Preferred Securities.
 
GENERAL
 
    Unless otherwise specified in the applicable Prospectus Supplement, the
Company will irrevocably and unconditionally agree to pay in full on a
subordinated basis, to the extent set forth herein, the Guarantee Payments (as
defined below) to the holders of the Preferred Securities, as and when due,
regardless of any defense, right of set-off or counterclaim that such IDACORP
Trust may have or assert other than the defense of payment. The following
payments or distributions, without duplication with respect to the Preferred
Securities, to the extent not paid by or on behalf of the related IDACORP Trust
(the "Guarantee Payments"), will be subject to the Guarantee: (i) any
accumulated and unpaid Distributions required to be paid on such Preferred
Securities, to the extent that such IDACORP Trust has funds on hand available
therefor at such time, (ii) the Redemption Price with respect to any Preferred
Securities called for redemption by the related IDACORP Trust to the extent that
such IDACORP Trust has funds on hand available therefor at such time, and (iii)
upon a voluntary or involuntary dissolution, winding up or liquidation of such
IDACORP Trust (unless the Corresponding Subordinated Debt Securities are
distributed to holders of such Preferred Securities), the lesser of (a) the
Liquidation Amount per Preferred Security plus accumulated and unpaid
Distributions and (b) the amount of assets of such IDACORP Trust remaining
available for distribution to holders of Preferred Securities. The Company's
obligation to make a Guarantee Payment may be satisfied by direct payment of the
required amounts by the Company to the holders of the applicable Preferred
Securities or by causing the IDACORP Trust to pay such amounts to such holders.
 
    Each Guarantee will be an irrevocable guarantee on a subordinated basis of
the related IDACORP Trust's obligations under the Preferred Securities, but will
apply only to the extent that such related IDACORP Trust has funds sufficient to
make such payments, and is not a guarantee of collection.
 
    If the Company does not make interest payments on the Corresponding
Subordinated Debt Securities held by the IDACORP Trust, the IDACORP Trust will
not be able to pay Distributions on the Preferred Securities and will not have
funds legally available therefor. Each Guarantee will rank subordinate and
junior in right of payment to all Senior Debt and Subordinated Debt of the
Company. See "-- Status of the Guarantees." The majority of the operating assets
of the Company and its consolidated subsidiaries are owned by such subsidiaries.
The Company relies primarily on dividends from such subsidiaries to meet its
obligations for payment of principal and interest on its outstanding debt
obligations and corporate expenses. Accordingly, the Company's obligations under
the Guarantees will be effectively subordinated to all existing and future
liabilities of the Company's subsidiaries, and claimants should look only to the
assets of the Company for payments thereunder. See "Description of the Debt
Securities--General." Except as otherwise provided in the applicable Prospectus
Supplement, the Guarantees do not limit the incurrence or issuance of other
secured or unsecured debt of the Company, whether under the Indentures, any
other
 
                                       37

indenture that the Company may enter into in the future or otherwise. See the
Prospectus Supplement relating to any offering of Preferred Securities.
 
    The Company has, through the applicable Guarantee, the applicable Trust
Agreement, the Subordinated Debt Securities and the Subordinated Indenture,
taken together, fully, irrevocably and unconditionally guaranteed all of each
IDACORP Trust's obligations under the Preferred Securities. No single document
standing alone or operating in conjunction with fewer than all of the other
documents constitutes such guarantee. It is only the combined operation of these
documents that has the effect of providing a full, irrevocable and unconditional
guarantee of the Issuer Trust's obligations under the Preferred Securities. See
"Relationship Among the Preferred Securities, the Corresponding Subordinated
Debt Securities and the Guarantees."
 
AMENDMENTS AND ASSIGNMENT
 
    Except with respect to any changes which do not adversely affect the rights
of holders of the related Preferred Securities in any material respect (in which
case no vote will be required), no Guarantee may be amended without the prior
approval of the holders of not less than a majority of the aggregate Liquidation
Amount of such outstanding Preferred Securities. The manner of obtaining any
such approval will be as set forth under "Description of Preferred
Securities--Voting Rights; Amendment of Each Trust Agreement." All guarantees
and agreements contained in each Guarantee shall bind the successors, assigns,
receivers, trustees and representatives of the Company and shall inure to the
benefit of the holders of the related Preferred Securities then outstanding.
 
EVENTS OF DEFAULT
 
    An event of default under each Guarantee will occur upon the failure of the
Company to perform any of its payment or other obligations thereunder, provided
that except for a payment default, the Company shall have received notice and
not have cured such default within 60 days. The holders of not less than a
majority in aggregate Liquidation Amount of the related Preferred Securities
have the right to direct the time, method and place of conducting any proceeding
for any remedy available to the Guarantee Trustee in respect of such Guarantee
or to direct the exercise of any trust or power conferred upon the Guarantee
Trustee under such Guarantee.
 
    If the Guarantee Trustee fails to enforce such Guarantee, any holder of the
Preferred Securities may institute a legal proceeding directly against the
Company to enforce its rights under such Guarantee without first instituting a
legal proceeding against the IDACORP Trust, or any other person or entity. If
the Company has failed to make a Guarantee Payment under a Guarantee, a record
holder of Preferred Securities to which such Guarantee relates may directly
institute a proceeding against the Company for enforcement of such Guarantee for
such payment. The Company has waived any right or remedy to require that any
action be brought first against the applicable IDACORP Trust or any other person
or entity before proceeding directly against the Company. The record holder in
the case of the issuance of one or more global Preferred Securities certificates
will be DTC acting at the direction of the beneficial owners of the Preferred
Securities.
 
    The Company, as guarantor, is required to file annually with the Guarantee
Trustee a certificate as to whether or not the Company is in compliance with all
the conditions and covenants applicable to it under the Guarantee.
 
INFORMATION CONCERNING THE GUARANTEE TRUSTEE
 
    The Guarantee Trustee, other than during the occurrence and continuance of a
default by the Company in performance of any Guarantee, undertakes to perform
only such duties as are specifically set forth in each Guarantee and, after
default with respect to any Guarantee, must exercise the same degree of care and
skill as a prudent person would exercise or use under the circumstances in the
conduct of his or
 
                                       38

her own affairs. Subject to this provision, the Guarantee Trustee is under no
obligation to exercise any of the powers vested in it by any Guarantee at the
request of any holder of any Preferred Securities unless it is offered
reasonable indemnity against the costs, expenses and liabilities that might be
incurred thereby.
 
TERMINATION OF THE GUARANTEES
 
    Each Guarantee will terminate and be of no further force and effect upon
full payment of the Redemption Price of the related Preferred Securities, upon
full payment of the amounts payable upon liquidation of the related IDACORP
Trust or upon distribution of Corresponding Subordinated Debt Securities to the
holders of the related Preferred Securities. Each Guarantee will continue to be
effective or will be reinstated, as the case may be, if at any time any holder
of the related Preferred Securities must repay any sums paid under such
Preferred Securities or such Guarantee.
 
GOVERNING LAW
 
    Each Guarantee will be governed by and construed in accordance with the laws
of the State of New York.
 
                  RELATIONSHIP AMONG THE PREFERRED SECURITIES,
                 THE CORRESPONDING SUBORDINATED DEBT SECURITIES
                               AND THE GUARANTEES
 
FULL AND UNCONDITIONAL GUARANTEE
 
    Payments of Distributions and other amounts due on the Preferred Securities
(to the extent the IDACORP Trust has funds available for the payment of such
Distributions) are irrevocably guaranteed by the Company as and to the extent
set forth under "Description of Guarantees." Taken together, the Company's
obligations under each series of Corresponding Subordinated Debt Securities, the
Subordinated Indenture, the related Trust Agreement and the related Guarantee
provide, in the aggregate, a full, irrevocable and unconditional guarantee of
payments of distributions and other amounts due on the related series of
Preferred Securities. No single document standing alone or operating in
conjunction with fewer than all of the other documents constitutes such
guarantee. It is only the combined operation of these documents that has the
effect of providing a full, irrevocable and unconditional guarantee of the
IDACORP Trust's obligations under the Preferred Securities. If and to the extent
that the Company does not make payments on any series of Corresponding
Subordinated Debt Securities, such IDACORP Trust will not pay Distributions or
other amounts due on its Preferred Securities. The Guarantees do not cover
payment of Distributions when the related IDACORP Trust does not have sufficient
funds to pay such Distributions. In such event, the remedy of a holder of a
series of Preferred Securities is to institute a legal proceeding directly
against the Company for enforcement of payment of such Distributions to such
holder. The obligations of the Company under each Guarantee are subordinate and
junior in right of payment to all Senior Indebtedness.
 
SUFFICIENCY OF PAYMENTS
 
    As long as payments of interest and other payments are made when due on each
series of Corresponding Subordinated Debt Securities, such payments will be
sufficient to cover Distributions and other payments due on the related
Preferred Securities, primarily because (i) the aggregate principal amount of
each series of Corresponding Subordinated Debt Securities will be equal to the
sum of the aggregate stated Liquidation Amount of the related Preferred
Securities and related Common Securities; (ii) the interest rate and interest
and other payment dates on each series of Corresponding Subordinated Debt
Securities will match the Distribution rate and Distribution and other payment
dates for the related Preferred Securities; (iii) the Company shall pay for all
and any costs, expenses and liabilities of such IDACORP
 
                                       39

Trust except the IDACORP Trust's obligations to holders of its Preferred
Securities under such Preferred Securities; and (iv) each Trust Agreement
further provides that the IDACORP Trust will not engage in any activity that is
not consistent with the limited purposes of such IDACORP Trust.
 
    Notwithstanding anything to the contrary in the Subordinated Indenture, the
Company has the right to set-off any payment it is otherwise required to make
thereunder with and to the extent the Company has theretofore made, or is
concurrently on the date of such payment making, a payment under the related
Guarantee.
 
ENFORCEMENT RIGHTS OF HOLDERS OF PREFERRED SECURITIES
 
    A holder of any Preferred Security may institute a legal proceeding directly
against the Company to enforce its rights under the related Guarantee without
first instituting a legal proceeding against the related IDACORP Trust or any
other person or entity.
 
    A default or event of default under any Senior Indebtedness of the Company
would not necessarily constitute a default under the Subordinated Indenture or
Trust Event of Default. However, in the event of payment defaults under, or
acceleration of, Senior Indebtedness of the Company, the subordination
provisions of the Subordinated Indenture provide that no payments may be made in
respect of the Corresponding Subordinated Debt Securities until such Senior
Indebtedness has been paid in full or any payment default thereunder has been
cured or waived. Failure to make required payments on any series of
Corresponding Subordinated Debt Securities would constitute a Trust Event of
Default.
 
LIMITED PURPOSE OF IDACORP TRUSTS
 
    Each IDACORP Trust's Preferred Securities evidence undivided beneficial
ownership interests in the assets of such IDACORP Trust, and each IDACORP Trust
exists for the sole purpose of issuing its Preferred Securities and Common
Securities, investing the proceeds thereof in Corresponding Subordinated Debt
Securities and engaging in only those other activities necessary, convenient or
incidental thereto. A principal difference between the rights of a holder of a
Preferred Security and a holder of a Corresponding Subordinated Debt Security is
that a holder of a Corresponding Subordinated Debt Security is entitled to
receive from the Company the principal amount of and interest accrued on
Corresponding Subordinated Debt Securities held, while a holder of Preferred
Securities is entitled to receive Distributions from such IDACORP Trust (or from
the Company under the applicable Guarantee) if and to the extent such IDACORP
Trust has funds available for the payment of such Distributions.
 
RIGHTS UPON DISSOLUTION
 
    Upon any voluntary or involuntary dissolution of any IDACORP Trust involving
the liquidation of the Corresponding Subordinated Debt Securities, the holders
of the related Preferred Securities will be entitled to receive, out of assets
held by such IDACORP Trust and, after satisfaction of creditors of such IDACORP
Trust as provided by applicable law, the Liquidation Distribution in cash. See
"Description of Preferred Securities--Liquidation Distribution Upon
Dissolution." Upon any voluntary or involuntary liquidation or bankruptcy of the
Company, the Property Trustee, as holder of the Corresponding Subordinated Debt
Securities, would be a subordinated creditor of the Company, subordinated in
right of payment to all Senior Indebtedness, but entitled to receive payment in
full of principal and interest, before any stockholders of the Company receive
payments or distributions. Since the Company is the guarantor under each
Guarantee and has agreed to pay for all costs, expenses and liabilities of each
IDACORP Trust (other than the IDACORP Trust's obligations to the holders of its
Preferred Securities), the positions of a holder of such Preferred Securities
and a holder of such Corresponding Subordinated Debt Securities relative to
other creditors and to stockholders of the Company in the event of liquidation
or bankruptcy of the Company are expected to be substantially the same.
 
                                       40

                              BOOK-ENTRY ISSUANCE
 
    The Debt Securities, Preferred Securities and Corresponding Subordinated
Debt Securities of a series may be issued in whole or in part in the form of one
or more Global Securities that will be deposited with, or on behalf of, the
Depository identified in the Prospectus Supplement relating to such series (the
"Book-Entry Securities"). Unless otherwise indicated in the applicable
Prospectus Supplement for such series, the Depository will be DTC. Book-Entry
Securities may be issued only in fully registered form and in either temporary
or permanent form. Unless and until it is exchanged in whole or in part for the
individual Book-Entry Securities represented thereby, a Book-Entry Security may
not be transferred except as a whole by the Depository for such Book-Entry
Security to a nominee of such Depository or by a nominee of such Depository to
such Depository or another nominee of such Depository or by the Depository or
any nominee to a successor Depository or any nominee of such successor.
 
    DTC has advised the Company as follows: DTC is a limited purpose trust
company organized under the New York Banking Law, a "banking organization"
within the meaning of the New York Banking Law, a member of the Federal Reserve
System, a "clearing corporation" within the meaning of the New York Uniform
Commercial Code, and a "clearing agency" registered pursuant to the provisions
of Section 17A of the Exchange Act. DTC holds securities that its Participants
deposit with DTC. DTC also facilitates the settlement among Participants of
securities transactions, such as transfers and pledges, in deposited securities
through electronic computerized book-entry changes in Participants' accounts,
thereby eliminating the need for physical movement of securities certificates.
Direct Participants include securities brokers and dealers, banks, trust
companies, clearing corporations and certain other organizations ("Direct
Participants"). DTC is owned by a number of its Direct Participants and by the
New York Stock Exchange, Inc., the American Stock Exchange, Inc. and the
National Association of Securities Dealers, Inc. Access to the DTC system is
also available to others such as securities brokers and dealers, banks and trust
companies that clear through or maintain custodial relationships with Direct
Participants, either directly or indirectly ("Indirect Participants"). The rules
applicable to DTC and its Participants are on file with the Commission.
 
    Purchases of Book-Entry Securities within the DTC system must be made by or
through Direct Participants, which will receive a credit for the Book-Entry
Securities on DTC's records. The ownership interest of each actual purchaser of
each Book-Entry Security ("Beneficial Owner") is in turn to be recorded on the
Direct and Indirect Participants' records. Beneficial Owners will not receive
written confirmation from DTC of their purchases, but Beneficial Owners are
expected to receive written confirmations providing details of the transactions,
as well as periodic statements of their holdings, from the Direct or Indirect
Participants through which the Beneficial Owners purchased Book-Entry
Securities. Transfers of ownership interests in the Book-Entry Securities are to
be accomplished by entries made on the books of Participants acting on behalf of
Beneficial Owners. Beneficial Owners will not receive certificates representing
their ownership interests in Book-Entry Securities, except in the event that use
of the book-entry system is discontinued. The laws of some states require that
certain purchasers of securities take physical delivery of such securities in
definitive form. Such limits and such laws may impair the ability to transfer
beneficial interests in a Global Security.
 
    To facilitate subsequent transfers, all Book-Entry Securities deposited by
Participants with DTC are registered in the name of DTC's partnership nominee,
Cede & Co. The deposit of Book-Entry Securities with DTC and their registration
in the name of Cede & Co. effect no change in beneficial ownership. DTC has no
knowledge of the actual Beneficial Owners of the Book-Entry Securities; DTC's
records reflect only the identity of the Direct Participants to whose accounts
such Book-Entry Securities are credited, which may or may not be the Beneficial
Owners. The Participants will remain responsible for keeping account of their
holdings on behalf of their customers.
 
    The Company and the IDACORP Trusts expect that conveyance of notices and
other communications by DTC to Direct Participants, by Direct Participants to
Indirect Participants, and by Direct Participants
 
                                       41

and Indirect Participants to Beneficial Owners and the voting rights of Direct
Participants, Indirect Participants and Beneficial Owners will be governed by
arrangements among them, subject to any statutory or regulatory requirements as
may be in effect from time to time.
 
    Redemption notices shall be sent to Cede & Co. as the registered holder of
the Book-Entry Securities.
 
    Although voting with respect to the Book-Entry Securities is limited to the
holders of record of the Book-Entry Securities, in those instances in which a
vote is required, neither DTC nor Cede & Co. will itself consent or vote with
respect to Book-Entry Securities. Under its usual procedures, DTC would mail an
omnibus proxy (the "Omnibus Proxy") to the relevant Trustee as soon as possible
after the record date. The Omnibus Proxy assigns Cede & Co.'s consenting or
voting rights to those Direct Participants to whose accounts such Book-Entry
Securities are credited on the record date (identified in a listing attached to
the Omnibus Proxy).
 
    As long as the Book-Entry Securities are held by DTC or its nominee and DTC
continues to make its same-day funds settlement system available to the Company,
all payments on the Book-Entry Securities (other than Preferred Securities or
Corresponding Subordinated Debt Securities) will be made by the Company in
immediately available funds to DTC. Distribution payments on the Preferred
Securities or the Subordinated Debt Securities will be made by the relevant
Trustee to DTC. The Company and the IDACORP Trusts have been advised that DTC's
practice is to credit Direct Participants' accounts on the relevant payment date
in accordance with their respective holdings shown on DTC's records unless DTC
has reason to believe that it will not receive payments on such payment date.
Payments by Participants to Beneficial Owners will be governed by standing
instructions and customary practices and will be the responsibility of such
Participant and not of DTC, the relevant Trustee, the IDACORP Trust (as
applicable) or the Company, subject to any statutory or regulatory requirements
as may be in effect from time to time. Payment on Book-Entry Securities to DTC
is the responsibility of the Company or the relevant Trustee (as applicable),
disbursement of such payments to Direct Participants is the responsibility of
DTC and disbursements of such payments to the Beneficial Owners is the
responsibility of Direct and Indirect Participants.
 
    Unless otherwise specified in the applicable Prospectus Supplement, if a
Depository for a series of Preferred Securities is at any time unwilling, unable
or ineligible to continue as depository and a successor depository is not
appointed by the Company within 90 days, the Company will issue individual
Preferred Securities of such series in exchange for the Global Security
representing such series of Preferred Securities. In addition, the Company may
at any time and in its sole discretion, subject to any limitations described in
the Prospectus Supplement relating to such Preferred Securities, determine not
to have any Preferred Securities of such series represented by one or more
Global Securities and, in such event, will issue individual Preferred Securities
of such series in exchange for the Global Security or Securities representing
such series of Preferred Securities. Further, if the Company so specifies with
respect to the Preferred Securities of a series, an owner of a beneficial
interest in a Global Security representing Preferred Securities of such series
may, on terms acceptable to the Company, the Property Trustee and the Depository
for such Global Security, receive individual Preferred Securities of such series
in exchange for such beneficial interests, subject to any limitations described
in the Prospectus Supplement relating to such Preferred Securities. In any such
instance, a Beneficial Owner in such Global Security will be entitled to
physical delivery of individual Preferred Securities of the series represented
by such Global Security equal in principal amount to such beneficial interest
and to have such Preferred Securities registered in its name. Individual
Preferred Securities of such series so issued will be issued in such
denominations as set forth in the accompanying Prospectus Supplement.
 
    DTC may discontinue providing its services as securities depository with
respect to Debt Securities at any time by giving reasonable notice to the
Company or the Indenture Trustee. Under such circumstances, if a successor
depository is not appointed by the Company within 90 days, the Company will
issue individual definitive Debt Securities in exchange for all the Global
Securities representing such Debt
 
                                       42

Securities. In addition, the Company may at any time and in its sole discretion
determine not to have the Debt Securities represented by Global Securities and,
in such event, will issue individual definitive Debt Securities in exchange for
all the Global Securities representing the Debt Securities. Individual
definitive Debt Securities so issued will be issued in denominations of $1,000
and any larger amount that is an integral multiple of $1,000 and registered in
such names as DTC shall direct.
 
    The information in this section concerning DTC and DTC's book-entry system
has been obtained from sources that the IDACORP Trusts and the Company believe
to be accurate, but the IDACORP Trusts and the Company assume no responsibility
for the accuracy thereof. Neither the IDACORP Trusts nor the Company has any
responsibility for the performance by DTC or its Participants of their
respective obligations as described herein or under the rules and procedures
governing their respective operations.
 
                              PLAN OF DISTRIBUTION
 
    The Company and/or any IDACORP Trust may sell the Securities in any one or
more of the following ways from time to time: (i) to or through underwriters or
dealers; (ii) directly to one or more purchasers; or (iii) through agents. The
Prospectus Supplement with respect to the Securities being offered thereby sets
forth the terms of the offering of such Securities, including the name or names
of any underwriters, the purchase price of such Securities and the proceeds to
the Company and/or an IDACORP Trust from such sale, any underwriting discounts
and other items constituting underwriters' compensation, any initial public
offering price, any discounts or concessions allowed or reallowed or paid to
dealers, and any securities exchange on which such Securities may be listed.
Only underwriters so named in the Prospectus Supplement are deemed to be
underwriters in connection with the Securities offered thereby.
 
    If underwriters are used in the sale, the Securities will be acquired by the
underwriters for their own account and may be resold from time to time in one or
more transactions, including negotiated transactions, at a fixed public offering
price or at varying prices determined at the time of sale. The obligations of
the underwriters to purchase such Securities will be subject to certain
conditions precedent, and the underwriters will be obligated to purchase all the
Securities of the series offered by the Company's and/or the applicable IDACORP
Trust's Prospectus Supplement if any of such Securities are purchased. Any
initial public offering price and any discounts or concessions allowed or
reallowed or paid to dealers may be changed from time to time.
 
    Securities may also be offered and sold, if so indicated in the Prospectus
Supplement, in connection with a remarketing upon their purchase, in accordance
with a redemption or repayment pursuant to their terms, by one or more firms
("remarketing firms") acting as principals for their own accounts or as agents
for the Company and/or an applicable IDACORP Trust. Any remarketing firm will be
identified and the terms of its agreement, if any, with the Company and its
compensation will be described in the Prospectus Supplement. Remarketing firms
may be deemed to be underwriters in connection with the Securities remarketed
thereby.
 
    Securities may also be sold directly by the Company and/or an IDACORP Trust
or through agents designated by the Company from time to time. Any agent
involved in the offering and sale of the Securities in respect of which this
Prospectus is delivered will be named, and any commissions payable by the
Company and/or an IDACORP Trust to such agent will be set forth, in the
Prospectus Supplement. Unless otherwise indicated in the Prospectus Supplement,
any such agent will be acting on a best efforts basis for the period of its
appointment.
 
    If so indicated in the Prospectus Supplement, the Company and/or an IDACORP
Trust will authorize agents, underwriters or dealers to solicit offers by
certain institutional investors to purchase Securities providing for payment and
delivery on a future date specified in the Prospectus Supplement. There may be
limitations on the minimum amount which may be purchased by any such
institutional investor or on the portion of the aggregate principal amount of
the particular Securities which may be sold pursuant to such arrangements.
Institutional investors to which such offers may be made, when authorized,
include
 
                                       43

commercial and savings banks, insurance companies, pension funds, investment
companies, educational and charitable institutions and such other institutions
as may be approved by the Company and/or an IDACORP Trust. The obligations of
any such purchasers pursuant to such delayed delivery and payment arrangements
will not be subject to any conditions except (i) the purchase by an institution
of the particular Securities shall not at the time of delivery be prohibited
under the laws of any jurisdiction in the United States to which such
institution is subject and (ii) if the particular Securities are being sold to
underwriters, the Company and/or an IDACORP Trust shall have sold to such
underwriters the total principal amount of such Securities less the principal
amount thereof covered by such arrangements. Underwriters will not have any
responsibility in respect of the validity of such arrangements or the
performance of the Company or such institutional investors thereunder.
 
    If any underwriter or any selling group member intends to engage in
stabilizing, syndicate short covering transactions, penalty bids or any other
transaction in connection with the offering of Securities that may stabilize,
maintain or otherwise affect the price of such Securities, such intention and a
description of such transactions will be described in the Prospectus Supplement.
 
    Agents and underwriters may be entitled under agreements entered into with
the Company and/or the applicable IDACORP Trust to indemnification by the
Company against certain civil liabilities, including liabilities under the
Securities Act of 1933, or to contribution with respect to payments which the
agents or underwriters may be required to make in respect thereof. Agents and
underwriters may engage in transactions with, or perform services for, the
Company and its subsidiaries in the ordinary course of business.
 
                                 LEGAL OPINIONS
 
    Unless otherwise indicated in the applicable Prospectus Supplement, certain
legal matters will be passed upon for the Company and the IDACORP Trusts by
Robert W. Stahman, Esq., Vice President, General Counsel and Secretary of the
Company, and by LeBoeuf, Lamb, Greene & MacRae, L.L.P.; for the IDACORP Trusts
by Richards, Layton & Finger, P.A., special Delaware counsel to the IDACORP
Trusts and the Company, and for any underwriter, dealer or agent by Sullivan &
Cromwell.
 
    As of October 1, 1998, Mr. Stahman owned 17,459 shares of Company Common
Stock and is acquiring additional shares at regular intervals through Company
employee benefit plans.
 
                                    EXPERTS
 
    The financial statements and the related financial statement schedule of
Idaho Power Company incorporated in this prospectus by reference from Idaho
Power Company's Annual Report on Form 10-K for the year ended December 31, 1997
have been audited by Deloitte & Touche LLP, independent auditors, as stated in
their report, which is incorporated herein by reference, and have been so
incorporated in reliance upon the report of such firm given upon their authority
as experts in accounting and auditing.
 
    With respect to the unaudited interim financial information of Idaho Power
Company for the periods ended March 31, 1998 and 1997 and June 30, 1998 and
1997, which is incorporated herein by reference, Deloitte & Touche LLP have
applied limited procedures in accordance with professional standards for a
review of such information. However, as stated in their reports included in
Idaho Power Company's Quarterly Reports on Form 10-Q for the quarters ended
March 31, 1998 and June 30, 1998, and incorporated by reference herein, they did
not audit and they do not express an opinion on that interim financial
information. Accordingly, the degree of reliance on their reports on such
information should be restricted in light of the limited nature of the review
procedures applied. Deloitte & Touche LLP are not subject to the liability
provisions of Section 11 of the Securities Act of 1933 for their reports on the
unaudited interim financial information because those reports are not "reports"
or a "part" of the registration statement prepared or certified by an accountant
within the meaning of Section 7 and 11 of the Act.
 
                                       44

                PART II. INFORMATION NOT REQUIRED IN PROSPECTUS
 
   
ITEM 16. EXHIBITS
    
 
   


  EXHIBIT
    NO.                                                   DESCRIPTION OF INSTRUMENT
- -----------             ---------------------------------------------------------------------------------------------
                  
 
       3.1          --  Articles of Incorporation of the Company.
 
       3.2          --  Articles of Amendment to Articles of Incorporation of the Company, as filed with the
                        Secretary of State of Idaho on March 9, 1998.
 
       4.1          --  Form of Indenture for Senior Debt Securities between the Company and Bankers Trust Company,
                        as Trustee. The form or forms of Senior Debt Securities with respect to each particular
                        offering will be filed as an exhibit to a Current Report on Form 8-K and incorporated herein
                        by reference.
 
       4.2          --  Form of Indenture for Subordinated Debt Securities between the Company and Bankers Trust
                        Company, as Trustee. The form or forms of Subordinated Debt Securities with respect to each
                        particular offering will be filed as an exhibit to a Current Report on Form 8-K and
                        incorporated herein by reference.
 
      4.10          --  Form of Amended and Restated Trust Agreement for IDACORP Trust I, II and III.
 
      4.12          --  Form of Guarantee Agreement for IDACORP Trust I, II and III.
 
      4.13          --  The Deposit Agreement between the Company and a bank or trust company selected by the Company
                        will be filed as an exhibit to a Current Report on Form 8-K and incorporated herein by
                        reference.
 
        23          --  Consent of Deloitte & Touche LLP.

    
 
                                      II-1

   
                                   SIGNATURES
    
 
   
    Pursuant to the requirements of the Securities Act of 1933, the registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-3 and has duly caused this amendment to the
Registration Statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in the City of Boise and State of Idaho, on the 3rd day of
November, 1998.
    
 

                               
                                IDACORP, INC.
 
                                By:            /s/ JOSEPH W. MARSHALL
                                     -----------------------------------------
                                                 Joseph W. Marshall
                                               CHAIRMAN OF THE BOARD
                                            AND CHIEF EXECUTIVE OFFICER

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


             NAME                         TITLE                    DATE
- ------------------------------  --------------------------  -------------------
                                                      
    /s/ JOSEPH W. MARSHALL      Chairman of the Board
- ------------------------------    and Chief Executive        November 3, 1998
     (Joseph W. Marshall)         Officer
 
     /s/ JAN B. PACKWOOD*
- ------------------------------  President, Chief Operating   November 3, 1998
      (Jan B. Packwood)           Officer and Director
 
                                Vice President, Chief
                                  Financial
      /s/ J. LAMONT KEEN          Officer and Treasurer
- ------------------------------    (Principal                 November 3, 1998
       (J. LaMont Keen)           Financial and Accounting
                                  Officer)
 
   /s/ ROBERT D. BOLINDER*
- ------------------------------  Director                     November 3, 1998
     (Robert D. Bolinder)
 
    /s/ ROGER L. BREEZLEY*
- ------------------------------  Director                     November 3, 1998
     (Roger L. Breezley)
 
     /s/ JOHN B. CARLEY*
- ------------------------------  Director                     November 3, 1998
       (John B. Carley)
 
    /s/ PETER T. JOHNSON*
- ------------------------------  Director                     November 3, 1998
      (Peter T. Johnson)
 
     /s/ JACK K. LEMLEY*
- ------------------------------  Director                     November 3, 1998
       (Jack K. Lemley)

    
 
                                      II-2

   


             NAME                         TITLE                    DATE
- ------------------------------  --------------------------  -------------------
                                                      
     /s/ EVELYN LOVELESS*
- ------------------------------  Director                     November 3, 1998
      (Evelyn Loveless)
 
      /s/ JON H. MILLER*
- ------------------------------  Director                     November 3, 1998
       (Jon H. Miller)
 
    /s/ PETER S. O'NEILL*
- ------------------------------  Director                     November 3, 1998
      (Peter S. O'Neill)
 
      /s/ GENE C. ROSE*
- ------------------------------  Director                     November 3, 1998
        (Gene C. Rose)
 
       /s/ PHIL SOULEN*
- ------------------------------  Director                     November 3, 1998
        (Phil Soulen)

    
 
   

                                                    
*By:     /s/ J. LAMONT KEEN
      -------------------------
           J. LaMont Keen
         (Attorney-in-fact)

    
 
                                      II-3

                                   SIGNATURES
 
   
    Pursuant to the requirements of the Securities Act of 1933, IDACORP Trust I,
IDACORP Trust II and IDACORP Trust III each certifies that it has reasonable
grounds to believe that it meets all of the requirements for filing on Form S-3
and has duly caused this amendment to the Registration Statement to be signed on
its behalf by the undersigned, thereunto duly authorized, in the City of Boise,
State of Idaho, on the 3rd day of November, 1998.
    
 

                                                  
                                             IDACORP TRUST I
 
                                             By: IDACORP, Inc., as Sponsor
 
                                             By                     /s/ J. LAMONT KEEN
                                                        ------------------------------------------
                                                                      J. LaMont Keen
                                                                      VICE PRESIDENT,
                                                                  CHIEF FINANCIAL OFFICER
                                                                       AND TREASURER
 
                                             IDACORP TRUST II
 
                                             By: IDACORP, Inc., as Sponsor
 
                                             By                     /s/ J. LAMONT KEEN
                                                        ------------------------------------------
                                                                      J. LaMont Keen
                                                                      VICE PRESIDENT,
                                                                  CHIEF FINANCIAL OFFICER
                                                                       AND TREASURER
 
                                             IDACORP TRUST III
 
                                             By: IDACORP, Inc., as Sponsor
 
                                             By                     /s/ J. LAMONT KEEN
                                                        ------------------------------------------
                                                                      J. LaMont Keen
                                                                      VICE PRESIDENT,
                                                                  CHIEF FINANCIAL OFFICER
                                                                       AND TREASURER

 
                                      II-4

                                 EXHIBIT INDEX
 
   


 EXHIBIT
   NO.                                        DESCRIPTION OF INSTRUMENT                                       PAGE
- ---------  -----------------------------------------------------------------------------------------------  ---------
                                                                                                      
     1.1   The Underwriting Agreement for Debt Securities and any selling agency or distribution agreement
             with any agent will be filed as an exhibit to a Current Report on Form 8-K and incorporated
             herein by reference..........................................................................
 
     1.2   The Underwriting Agreement for equity securities will be filed as an exhibit to a Current
             Report on Form 8-K and incorporated herein by reference......................................
 
     1.3   The Underwriting Agreement for Preferred Securities will be filed as an exhibit to a Current
             Report on Form 8-K and incorporated herein by reference......................................
 
    *2     Agreement and Plan of Exchange, dated as of February 2, 1998 (filed as Exhibit 2, File No.
             333-48031)...................................................................................
 
     3.1   Articles of Incorporation of the Company.......................................................
 
     3.2   Articles of Amendment to Articles of Incorporation of the Company, as filed with the Secretary
             of State of Idaho on March 9, 1998...........................................................
 
    *3.3   Articles of Amendment to Restated Articles of Incorporation creating A Series Preferred Stock,
             without par value, as filed with the Secretary of State of Idaho on September 17, 1998 (filed
             as Exhibit 3(b), File No. 333-00139).........................................................
 
    *3.4   Amended Bylaws of the Company as of September 10, 1998 (filed as Exhibit 3(c), File No.
             333-48031)...................................................................................
 
    *3.5   Articles of Share Exchange, as filed with the Secretary of State of Idaho on September 29, 1998
             (filed as Exhibit 3(d), File No. 33-56071)...................................................
 
     4.1   Form of Indenture for Senior Debt Securities between the Company and Bankers Trust Company, as
             Trustee. The form or forms of Senior Debt Securities with respect to each particular offering
             will be filed as an exhibit to a Current Report on Form 8-K and incorporated herein by
             reference....................................................................................
 
     4.2   Form of Indenture for Subordinated Debt Securities between the Company and Bankers Trust
             Company, as Trustee. The form or forms Subordinated Debt Securities with respect to each
             particular offering will be filed as an exhibit to a Current Report on Form 8-K and
             incorporated herein by reference.............................................................
 
    *4.3   Rights Agreement, dated as of September 10, 1998, between the Company and the Bank of New York,
             as Rights Agent (filed as Exhibit 4 to the Company's Form 8-K dated September 15, 1998)......
 
   **4.4   Certificate of Trust of IDACORP Trust I........................................................
 
   **4.5   Trust Agreement of IDACORP Trust I.............................................................
 
   **4.6   Certificate of Trust of IDACORP Trust II.......................................................
 
   **4.7   Trust Agreement of IDACORP Trust II............................................................
 
   **4.8   Certificate of Trust of IDACORP Trust III......................................................
 
   **4.9   Trust Agreement of IDACORP Trust III...........................................................
 
     4.10  Form of Amended and Restated Trust Agreement for IDACORP Trust I, II and III...................
 
   **4.11  Form of Preferred Security Certificate for IDACORP, IDACORP II and IDACORP III (included as
             Exhibit D of Exhibit 4.10)...................................................................
 
     4.12  Form of Guarantee Agreement for IDACORP Trust I, II and III....................................
 
     4.13  The Deposit Agreement between the Company and a bank or trust company selected by the Company
             will be filed as an exhibit to a Current Report on Form 8-K and incorporated herein by
             reference....................................................................................
 
   **5.1   Opinion and consent of Robert W. Stahman, Esq..................................................
 
   **5.2   Opinion and consent of LeBoeuf, Lamb, Greene & MacRae, L.L.P...................................

    



 EXHIBIT
   NO.                                        DESCRIPTION OF INSTRUMENT                                       PAGE
- ---------  -----------------------------------------------------------------------------------------------  ---------
                                                                                                      
   **5.3   Opinion and consent of Richards, Layton & Finger, P.A., as to legality of the Preferred
             Securities to be issued by IDACORP Trust I...................................................
 
   **5.4   Opinion and consent of Richards, Layton & Finger, P.A., as to legality of the Preferred
             Securities to be issued by IDACORP Trust II..................................................
 
   **5.5   Opinion and consent of Richards, Layton & Finger, P.A., as to legality of the Preferred
             Securities to be issued by IDACORP Trust III.................................................
 
   **8     Tax Opinion of LeBoeuf, Lamb, Greene & MacRae, L.L.P., if any, will be filed as an exhibit to a
             Current Report on Form 8-K and incorporated herein by reference..............................
 
  **12.1   Computation of Idaho Power Company Ratios of Earnings to Fixed Charges.........................
 
  **12.2   Computation of Idaho Power Company Supplemental Ratios of Earnings to Fixed Charges............
 
  **12.3   Computation of Idaho Power Company Ratios of Earnings to Combined Fixed Charges and Preferred
             Stock Dividend Requirements..................................................................
 
  **12.4   Computation of Idaho Power Company Supplement Ratios of Earnings to Combined Fixed Charges and
             Preferred Stock Dividend Requirements........................................................
 
  **15     Letter from Deloitte & Touche LLP regarding unaudited interim financial information............
 
    23     Consent of Deloitte & Touche LLP...............................................................
 
  **24     Power of Attorney..............................................................................
 
  **25.1   Form T-1, Statement of Eligibility under the Trust Indenture Act of 1939 of Bankers Trust
             Company, Trustee, under the Indenture dated as of            , 1998 pursuant to which Senior
             Debt Securities may be issued................................................................
 
  **25.2   Form T-1, Statement of Eligibility under the Trust Indenture Act of 1939 of Bankers Trust
             Company under the Subordinated Indenture dated as of            , 1998 pursuant to which
             Subordinated Debt Securities may be issued...................................................
 
  **25.3   Form T-1, Statement of Eligibility under the Trust Indenture Act of 1939 of Bankers Trust
             Company to act as trustee under the Amended and Restated Trust Agreement of IDACORP Trust
             I............................................................................................
 
  **25.4   Form T-1, Statement of Eligibility under the Trust Indenture Act of 1939 of Bankers Trust
             Company to act as trustee under the Amended and Restated Trust Agreement of IDACORP Trust
             II...........................................................................................
 
  **25.5   Form T-1, Statement of Eligibility under the Trust Indenture Act of 1939 of Bankers Trust
             Company to act as trustee under the Amended and Restated Trust Agreement of IDACORP Trust
             III..........................................................................................
 
  **25.6   Form T-1, Statement of Eligibility under the Trust Indenture Act of 1939 of Bankers Trust
             Company under the Guarantee for the benefit of the holders of Preferred Securities of IDACORP
             Trust I......................................................................................
 
  **25.7   Form T-1, Statement of Eligibility under the Trust Indenture Act of 1939 of Bankers Trust
             Company under the Guarantee for the benefit of the holders of Preferred Securities of IDACORP
             Trust II.....................................................................................
 
  **25.8   Form T-1, Statement of Eligibility under the Trust Indenture Act of 1939 of Bankers Trust
             Company under the Guarantee for the benefit of the holders of Preferred Securities of IDACORP
             Trust III....................................................................................

 
- ------------------------
 
*   Incorporated herein by reference.
 
**  Previously filed with this Registration Statement.