Background: The ever-growing power dissipation and subsequent increase in device temperatures of miniaturized electronics have necessitated the development of enhanced cooling technologies. Microchannel heat sinks (MCHS) offer high surface-area-to-volume ratios, providing an advantage in terms of high heat transfer performance. Traditional coolants, on the other hand, may not be sufficient for handling high heat fluxes. Nanofluids (engineered colloidal suspensions of nano-sized particles in the carrier fluids) have gained a lot of attention owing to their improved thermal conductivity and improved convective behaviour. Objectives: In this paper, the thermal and hydraulic performance of MCHS with nanofluid was investigated to improve heat transfer and decrease pressure drop. It aims at examining the effect of nanoparticle type, concentration, and the microchannel geometry on the cooling performance under laminar flow situations. Methods: A three-dimensional computational fluid dynamics (CFD) model was constructed with COMSOL Multiphysics to predict heat and fluid transfer in MCHS. Two hybrid nanofluids, i.e., Fe₃O₄-MoS₂ and Al₂O₃-Fe₃O₄ (both with 1% particle volume fraction), were investigated at different Reynolds numbers. Performance indices considered in the study were Nusselt number, maximum surface temperature, pumping power, and heat sink evaluation coefficient. Mesh independence and boundary conditions were checked according to experimental benchmarks. Results: The Fe₃O₄-MoS₂ hybrid nanofluid provided the best thermal results, showing a 0.5% decrease in maximum surface temperature and a 3.2% increase in overall heat transfer rate compared to the Al₂O₃-based nanofluids. Up to 18% higher heat transfer rates were provided by circular microchannel geometries than triangular form profiles. As an offset for the improved thermal performance, a 9% penalty on pumping power was also incurred. Conclusions: The enhancement in MCHS cooling performance is substantial in the