PURPOSE: To improve the withstand voltage of a semiconductor device and to reduce the operating resistance of the device by oxidizing the surfaces of diffused regions of different conductive types in a semiconductor epitaxial layer with the electrode leading part and a diffusion window and contacting hole forming region allowed to remain.

CONSTITUTION: A P type diffused region 3' formed with an N type epitaxial layer 2 on a P type silicon substrate 1 is formed to reach the substrate 1. Then, the contacting part of the region 3' and the diffusing window forming region of an N type diffused region to be layer are covered with a silicon nitrided film 13 and are allowed to remain, recesses 14 are selectively formed, and a silicon oxidized layer 9 is then formed. Thereafter, an N type density impurity layer and electrodes are formed.