Abstract: An electroformed microchannel cooler for liquid cooling has an upper component and a lower component. Each component includes a sheet, a plurality of electroformed partition walls and a boundary wall electroformed outwardly of the plurality of partition walls. The partition and boundary walls of the upper component are attached to the boundary and partition walls of the lower part to provide a plurality of microchannels for flowing liquid through the cooler in a heat exchange relationship. One of the components has gates at each end opening into plenums inside the boundary walls. An alternate embodiment has a corrugated electroformed member attached to upper an lower sheets forming a plurality of parallel microchannels. Methods of making the electroformed microchannel coolers are also disclosed.