Theoretical comparisons of the performances of copper and silicon microchannel coolers are presented. The fabrication and testing of copper microchannel coolers with microchannel passage widths of 32 μm and 63.5 μm is described. Both a straight channel and a jet impingement design were built. The thermal performance of the copper coolers is shown to be slightly higher than that of comparable silicon coolers at greatly reduced pumping powers. The jet impingement design is shown to perform better than the straight channel design.