A semiconductor device of an embodiment includes first and second semiconductor layers having different conductivity types; a third semiconductor layer interposed between the first and second semiconductor layers; and a fourth semiconductor layer interposed between the second and third semiconductor layers, having a lower doping concentration than that of the first semiconductor layer and the same conductivity type as the first semiconductor layer, wherein the difference in doping concentration between the first semiconductor layer and the fourth semiconductor layer may be greater than 4×E18 atoms/cm3.