The present invention makes it possible, in a manufacturing process of a semiconductor device, to inhibit: impurities from diffusing from a substrate to a semiconductor layer; and the withstand voltage of a transistor from deteriorating.In the present invention, a first electrically conductive type epitaxial layer is formed over a first electrically conductive type base substrate. The impurity concentration of the epitaxial layer is lower than that of the base substrate. A second electrically conductive type first embedded layer and a second electrically conductive type second embedded layer are formed in the epitaxial layer. The second embedded layer is deeper than the first embedded layer, is kept away from the first embedded layer, and has an impurity concentration lower than the first embedded layer. A transistor is further formed in the epitaxial layer.