The optimization of the microchannel heat sink (MCHS) with offset oblique fins and the comparison of the optimized MCHS with various different MCHS are discussed. The three-dimensional analysis of convective heat transfer through the microchannels was performed numerically using Navier-Stokes equations along with the analysis of heat conduction in the substrate. Adiabatic boundary conditions were applied at the inlet and outlet portions of silicon while fluid inlet temperature was taken as 300 K. It was observed that the changes in pumping power and thermal resistance were about 5 and 1%, respectively, for a change of grids from 600,000 hexahedral elements to 1,800,000 hexahedral elements. The analysis showed that the changes in pumping power and thermal resistance were commonly about 1% for a change of grids from 1,800,000 elements to 2,600,000 elements for the typical grid analysis with the design variables α = 0.450, β = 0.333, γ = 0.500, and θ = 0°.