A semiconductor device comprises a single crystal substrate, a nucleus formation buffer layer formed on the single crystal substrate, and a lamination layer including a plurality of Al_1-x-yGa_xIn_yN (0x1, 0y1, x+y1) layers laminated above the nucleus formation buffer layer. The nucleus formation buffer layer is formed of Al_1-s-tGa_sIn_tN (0s1, 0t1, s+t1) and is formed on a surface of the substrate such that the nucleus formation buffer layer has a number of pinholes for control of polarity and formation of nuclei. A method of fabricating a semiconductor device comprises the steps of: forming, above an Al_1-x-yGa_xIn_yN (0x1, 0y1, x+y1) semiconductor layer doped with a p-type dopant, a cap layer for preventing evaporation of a constituent element of the semiconductor layer, the cap layer being formed of one of AlN in which a p-type dopant is added and Al₂O₃, subjecting the semiconductor layer to heat treatment, and removing at least a part of the cap layer.