Mr. David Cates reports

DENISON ANNOUNCES GRID POWER AVAILABLE AT FUTURE PHOENIX URANIUM MINE SITE FOLLOWING COMPLETION OF SASKPOWER TRANSMISSION LINE

Denison Mines Corp. has grid power supply available at the site of the future Phoenix in situ recovery uranium mine following the recent installation of a new 138-kilovolt Saskatchewan Power Corp. transmission line. The availability of grid power at the Phoenix site represents a significant step in derisking the execution of the project, as the electrification of the site is on the critical path of activities planned for the first year of construction and supports the establishment of the freeze wall planned to surround the initial mining area.

David Cates, president and chief executive officer of Denison, commented: "We thank SaskPower for the safe installation of the new high-voltage transmission line, on schedule and on budget. As power is a crucial component of planned site infrastructure for project construction and future operation, the availability of grid power supply at the site represents a major project milestone. Access to grid electricity is a notable competitive advantage for Phoenix, as the grid in Saskatchewan is reliable and cost-effective compared to on-site power generation."

The new transmission line is approximately six kilometres in length and connects the Phoenix site to the existing 138 kV transmission line east of Phoenix that runs proximal to Highway 914 near Russell Lake. This portion of the Saskatchewan grid provides power from the Saskatchewan-Manitoba border to Uranium City in northwestern Saskatchewan and currently supplies power to each of the operating uranium mine and mill sites in the eastern portion of the Athabasca basin.

Completion of the high-voltage transmission line represents a major project milestone

Phoenix has been designed to be powered by electricity from the SaskPower grid. Accordingly, the installation and electrification of the new 138 kV transmission line to the Phoenix site represents a significant derisking event, as the electrification of the Phoenix site will now only require the installation of on-site electrical distribution infrastructure, including the main site transformer, substation high-voltage equipment, switchgear and substation e-house -- all of which are long-lead items that have been procured and are on schedule for delivery to site and installation during the first year of construction.

SaskPower is Saskatchewan's principal electrical utility, reliably servicing over a half million customers across an extensive geographic area, including connections to the grids in Manitoba, Alberta and North Dakota. SaskPower obtained applicable approvals for and installed their transmission line to support a power supply agreement with Denison, whereby Denison has obtained access to up to 8.8 megawatts of power and agreed to purchase a minimum amount of power for a five-year period from the in-service date of the new transmission line. The cost of the new transmission line was financed by the Wheeler River joint venture.

The commencement of Phoenix construction activities by Denison, including the installation of on-site electrical distribution equipment, remains subject to receipt of final regulatory approvals and a final investment decision by Denison.

About Wheeler River

Wheeler River is the largest undeveloped uranium project in the infrastructure-rich eastern portion of the Athabasca basin region, in Northern Saskatchewan. The project is host to the high-grade Phoenix and Gryphon uranium deposits, discovered by Denison in 2008 and 2014, respectively, and is a joint venture between Denison (90 per cent and operator) and JCU (Canada) Exploration Company Ltd. (JCU, 10 per cent). In August, 2023, Denison filed a technical report summarizing the results of (i) Phoenix FS; and (ii) a cost update to the 2018 prefeasibility study for conventional underground mining of the basement-hosted Gryphon uranium deposit. Based on the respective studies, both deposits have the potential to be competitive with the lowest-cost uranium mining operations in the world. Permitting efforts for the planned Phoenix ISR operation commenced in 2019 and are nearing completion with approval in July, 2025, of the project's EA by the Province of Saskatchewan and conclusion in December, 2025, of the Canadian Nuclear Safety Commission public hearing for federal approval of the EA and project construction licence. More information is available in the technical report titled "NI 43-101 Technical Report on the Wheeler River Project Athabasca Basin, Saskatchewan, Canada," dated Aug. 8, 2023, with an effective date of June 23, 2023, a copy of which is available on Denison's website and under its profile on SEDAR+ and on EDGAR.

About Denison Mines Corp.

Denison is a leading uranium mining, development and exploration company with interests focused in the Athabasca basin region of Northern Saskatchewan, Canada. In addition to Denison's effective 95-per-cent interest in its flagship Wheeler River project, Denison's interests in Saskatchewan include a 22.5-per-cent ownership interest in the McClean Lake joint venture (MLJV), which includes unmined uranium deposits (with mining at McClean North deposit via the MLJV's Sabre mining method having commenced in July, 2025, using the MLJV's Sabre mining method) and the McClean Lake uranium mill (currently utilizing a portion of its licensed capacity to process the ore from the Cigar Lake mine under a toll milling agreement), plus a 25.17-per-cent interest in the Midwest joint venture Midwest Main and Midwest A deposits, and a 70.55-per-cent interest in the Tthe Heldeth Tue (THT) and Huskie deposits on the Waterbury Lake property. The Midwest Main, Midwest A, THT and Huskie deposits are located within 20 kilometres of the McClean Lake mill. Taken together, Denison has direct ownership interests in properties covering approximately 457,000 hectares in the Athabasca basin region.

Additionally, through its 50-per-cent ownership of JCU, Denison holds interests in various uranium project joint ventures in Canada, including the Millennium project (JCU, 30.099 per cent), the Kiggavik project (JCU, 33.8118 per cent) and Christie Lake (JCU, 34.4508 per cent).

In 2024, Denison celebrated its 70th year in uranium mining, exploration and development, which began in 1954 with Denison's first acquisition of mining claims in the Elliot Lake region of Northern Ontario.

Technical disclosure and qualified person

The technical information contained in this press release has been reviewed and approved by Chad Sorba, PGeo, Denison's vice-president, technical services and project evaluation, who is a qualified person in accordance with the requirements of National Instrument 43-101.

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