Increase in heat fluxes as a result of the miniaturization of power electronics demands new thermal management solutions such as liquid cooling, because of its high heat extraction capabilities. This work describes a new silicon-based heat sink that takes advantage of the high heat extraction capability of microchannel liquid-cooling at low power consumption by co-designing the heat sink and the electronics. A simple combination of cleanroom microfabricated silicon and laser-cutting of plastics was employed to make a microchannel heat sink that simultaneously cools down 20 active devices (hotspots) of a power electronic converter. By flowing liquid close to the active devices through narrow microchannels, we show that the power requirements of the pump can be minimized, resulting in a compact cooling system that allows integration with small and energy-efficient micropumps. The manifold microchannel heatsink is demonstrated on a ultra-high power density magnetic-less 10x-step-up DC/DC converter resulting in a smaller volume and higher cooling capability than conventional heat sinks. The converter was tested up to an output power of 1.2 kW, with an overall efficiency of 96%, and an average temperature rise of only 12.6 degrees C. The converter and heatsink occupy a volume of 260 mL, resulting in a maximum demonstrated power density of 4.62 W/cm(3), and a potential to reach a power density up to 26.9 W/cm(3).