100 denotes a GaN substrate of a thickness not less than 10 ??m which is grown on an auxiliary substrate made of a material other than nitride semiconductor, for example a substrate made of such material as sapphire, spinel, SiC, Si, GaAs and ZnO. The auxiliary substrate may be removed after the GaN substrate 100 is formed as shown in FIG. 3, or may be left to remain thereon and used without remov