Abstract: The thermal resistance ofmicrochannel heatsink is theoretically analyzed. an Oxygen - free coppermicrochannel heat2 sink consisting of five copper sheets is designed and fabricated. By testing, the uniformity of the face temperature of the microchannel heatsink is good. and the therma resistance l is 0. 645℃/W . the output power of the high power semiconductor diode laser linear arrays packaged with the microchannel heatsink is 38. 5W.