This paper aims to study the overall performance of circular and zig-zag square microchannel heat sinks with single phase liquid flow via a numerical parametric study. Thermal resistance and pressure drop when subjected to key geometric parameters such as hydraulic diameter, orientation, and connector length is numerically investigated with Reynolds number ranging from 50 to 500. Specifically, the hydraulic diameter is varied from 100 μm to 300 μm with an increment of 100 μm; the orientation angle of 10°, 20° and 30° is studied. A figure of merit (FOM) involving both the thermal resistance and pressure drop is introduced to evaluate the performance. Results show that hydraulic diameter is critical to thermal resistance and pressure drop compared to orientation angle. Zig-zag microchannel heat sink shows better performance compared with heat sinks with circular microchannel. FOM varies considerably with the change in hydraulic diameter and flow rate.