Abstract: In step S103, a gallium nitride semiconductor layer 13 is grown on an n-type GaN substrate 11. In step S104, a PL spectrum for the gallium nitride based semiconductor layer in a wavelength region including the yellow band of wavelength and the band edge wavelength of the gallium nitride based semiconductor is measured at room temperature. In step S106, a screened epitaxial substrate E1 is prepared through selection based on comparison of the photoluminescence spectrum intensity in the yellow band of wavelength and the band edge wavelength with a reference value. In step S107, an electrode 15 for an electron device is formed on the screened epitaxial substrate 13.