PURPOSE: To suppress the variation and dispersion of resistance values of a diffused resistor by including the process of forming an oxidation resistant film so as to cover at least the entire body of the diffused resistance region.

CONSTITUTION: A diffused resistance region 12 is formed by selectively introducing a P type impurity into an N type epitaxial layer 11 formed on a P type semiconductor substrate (not illustrated) by an ion implantation method or a thermal diffusion method. An oxide film 13 is formed on the epitaxial layer 11, and then electrode contact regions C and D are exposed by opening electrode windows by photoetching method. A polycrystalline Si film 14 is formed on the oxide film 13 and the electrode contact regions C and D by a CVD method. Next, the oxidation resistant film 15 is formed by a CVD method and photoetched to selectively oxide the polycrystalline Si film 14. This oxidation resistant film 15 is a nitride film or an oxynitride film and covers at least the entire body of the resistant diffused region. When the thermal oxidation of the polycrystalline Si film 14 is performed, the part uncovered with the oxidation resistant film 15 turns an oxide film and then becomes an integral body with the oxide film 13, resulting in the formation of an oxide film 16.