Liquid-cooled heat sink (cold plate) used for power electronics cooling is numerically studied. Thermal performance and hydraulic resistance are analyzed, with emphasis on geometric construction of cooling channels. Two heat transfer enhancing channel shapes are investigated, such as alternating elliptical channel and alternating rectangular channel (AR-C). Their performances are compared with that of three traditional straight channel shapes, as straight circular channel, straight elliptical channel, and straight rectangular channel. A heat sink with uniform and discrete heat sources is studied. Thermal and hydraulic characteristics in the heat sink are simulated using computational fluid dynamics approach, with water as coolant. The results show that the AR-C has the highest thermal performance with a little penalty on pressure drop, considering fixed channel hydraulic diameter and coolant volumetric flow rate. Geometry optimization is investigated for the AR-C, as well as the effect of channel density. It is found that higher channel density can improve both thermal performance and hydraulic resistance. It is concluded that alternating channel can improve cold plate performance and should be taken into application to power electronics cooling.