PURPOSE: To improve concentration gradient of impurities in the interface of epitaxial layers different in concentration, obtain steep concentration gradient, and increase the effective thickness of a low concentration epitaxial layer, in the forming method of an epitaxial layer composed of a high concentration epitaxial layer and a low concentration epitaxial layer.

CONSTITUTION: After a high concentration epitaxial layer 13 is formed by vapor epitaxial growth using reaction gas which contains high concentration impurities, an epitaxial layer 14 which does not contain impurities is formed by vapor epitaxial growth using reaction gas which does not contain impurities. In another case, an epitaxial layer (not shown in the figure) which contains a little impurities is formed by vapor epitaxial growth using reaction gas which contains a little impurities. After that, by epitaxial growth using reaction gas which contains low concentration impurities, a low concentration epitaxial layer 15 is formed, and an epitaxial layer 12 is formed on a substrate 1.