Mr. David Cates reports

DENISON ANNOUNCES COMPLETION OF SITE PREPARATION ACTIVITIES AND COMMENCEMENT OF FULL-SCALE CONSTRUCTION AT PHOENIX ISR URANIUM MINE

Activities at Denison Mines Corp.'s Phoenix in situ recovery (ISR) uranium mine have transitioned from site preparations to full-scale construction, including initiation of the perimeter freeze wall installation for phase 1 of the mine.

Since the commencement of site preparation and early works in March, 2026, significant progress has been made by Denison and its construction partners to complete several critical site preparation activities -- including substantial completion of site clearing activities, advancement of schedule-sensitive site civil works and the establishment of construction management facilities. Preparation activities also involved the installation and commissioning of temporary construction camp facilities, which significantly increases the accommodation capacity of the Wheeler River property to nearly 400 people and allows a ramp-up in the on-site work force.

Additionally, aggregate production required for various site civil purposes continues at a nearby quarry and the concrete batch plant has been mobilized to site. Schedule-critical concrete-related activities for the substation and the main process plant foundations are currently expected to commence in August.

David Cates, president and chief executive officer of Denison, commented: "Completing the site-preparation activities needed to ramp up our on-site workforce and achieve a full-scale rate of construction is an important initial milestone for the Phoenix project.

"Site civil work has progressed well during the early works program, with 20-plus per cent of overall site civil work estimated to be completed to date. Importantly, we have achieved near 100-per-cent completion of civil subgrade work for the process plant and well field areas, which is needed to facilitate the planned concrete pour for the plant and the initiation of the freeze wall installation program.

"Construction activity is expected to accelerate through the remainder of the summer months with the commencement of a second shift, which means seasonally sensitive civil and other construction work can continue virtually 24 hours a day in support of the completion of our key first-year construction milestones -- including concrete pours of the foundations for the process plant and main power transformer, installation of the freeze wall, as well as earth works for the airstrip and on-site power distribution.

"Achieving these positive early results demonstrates the readiness and commitment of Denison and our construction partners as we advance this unique nation-building project to become Canada's first new large-scale uranium mine since Cigar Lake."

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. Wheeler River 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 feasibility study; 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, culminating in the July, 2025, approval of the project's environmental assessment (EA) by the province of Saskatchewan and the February, 2026, approval of the project's EA and the grant of the construction licence by the Canadian Nuclear Safety Commission. Full-scale construction commenced for Phoenix in July, 2026. 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, and an update to estimated Phoenix initial capital costs described in Denison's annual information form dated March 30, 2026, copies of which are available on Denison's website and under its profile on SEDAR+ and on EDGAR.

About Denison Mines Corp.

Denison is a leading uranium exploration and development 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 uranium deposits (with mining at the McClean North deposit having commenced in 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 (Canada) Exploration Company, 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.

We seek Safe Harbor.