PURPOSE: To increase the electron mobility of a semiconductor device by forming a crystal defect in the boundary between an electron supply layer and a channel layer, accelerating and diffusing N type impurity in the channel layer, and then forming and allowing electrodes, thereby reducing the contacting resistance.

CONSTITUTION: An electron supply layer 4 made of N type AlGaAs single crystal is used as an upper layer, a channel layer 2 made of GaAs single crystal substantially having no impurity is used as a lower layer, proton (H+) is implanted in the vicinity of the boundary between the layers 4 and 2 of source and drain forming region, thereby forming a crystal defect, N type impurity is accelerated and diffused from the layer 4 into the layer 2 of the source and drain forming region, and source and drain electrodes 9 are then formed and alloyed. In this manner, a high electron mobility transistor of low contacting resistance of the source and drain regions can be formed.