A novel complementary metal oxide semiconductor (CMOS) compatible microchannel heat sink is designed and fabricated for monolithic liquid cooling of electronic circuits. The microchannels are fabricated with full metal walls between adjacent channels with a polymer top layer for easy sealing and optical visibility of the channels. The use of polymer also provides flexibility in adjusting the width of the channels allowing better management of the pressure drop. The proposed microchannel heat sink requires no design change of the electronic circuitry underneath, hence, can be produced by adding a few more steps to the standard CMOS fabrication flow. The rnicrochannel heat sinks were tested successfully under various heat flux and coolant flow rate conditions. The preliminary cooling tests indicate that the proposed design is promising as a monolithic liquid cooling solution for CMOS circuits.