A microchannel heat sink (MCHS) is a compact, effective cooling device that meets the heat dissipation requirements of high-power electronic equipment. This paper investigates the impact of utilizing Al₂O₃/water, MgO/water, and TiO₂/water nanofluids in a rectangular MCHS. To ensure an acceptable comparison, the flow rate is kept constant at 2 m/s. The heat sink base is subjected to 90W of steady heat dissipation, which produces the desired performance result. The vol. concentration of nanofluids ranges from 0 to 8%. The study covers a wide range of MCHS geometries; channel height (H_ch) and its width (W_ch) ranging from 200 to 800 μm and 100–500 μm respectively. The problem is modeled, validated, and analyzed. The use of nanofluids maximizes the heat transfer performance to 24.95% and minimizes thermal resistance and total entropy generation (TEG) to 15.01%, and 19.96% respectively. TEG decreases to 53.15% when H_ch increases and the same increases to 198% when W_ch increases. Nanofluids at highest vol. concentration as well as increase in H_ch and W_ch penalize the system maximum by demanding more pumping power (Ω) by 25.58%, 173.36%, and 39% respectively. Al₂O₃/water and MgO/water nanofluids deliver better performance and are recommended for future applications. Finally, the authors suggest concentration and geometric parameter ranges for optimality of the thermal performance.