GaN substrate storing method

The present invention relates to a method of storing GaN substrates. To provide a method for storing a GaN substrate for manufacturing semiconductor devices of favorable properties. In the GaN substrate storing method, GaN substrate (1) is stored in an atmosphere having an oxygen concentration of 18 vol.% Or less of water vapor and / or concentration of 12g / m3 or less of. The surface roughness Ra of the surface roughness Ra of the first principal surface and a second main surface on a GaN substrate stored by the storing method are not greater than 20nm and not larger than 20μm. Further, embodiments of the GaN substrate so that the main surface of the (0001) plane is formed off-axis angle, the off-axis angle of 0.05 ° to the direction of 2 °, and in a direction of 0 ° to 1 °.