To provide a method for depositing a GaN-based compound semiconductor layer having a low crystal defect density and almost free from production of piezo spontaneous polarization.

The method for depositing the GaN-based compound semiconductor layer includes steps of: (A) forming a plurality of seed layers 11 each comprising a GaN-based compound semiconductor on the R face of a sapphire substrate 10 in a mutually separated state; (B) epitaxially growing GaN-based compound semiconductor layers 12, 14, in which a crest plane is an A plane and which are nearly parallel to the R plane of the sapphire substrate 10, in a horizontal direction from each seed layer 11; and (C) polishing the crest plane 14A of the GaN-based compound semiconductor layers 12, 14 so as to make it into an inclined state with respect to the R plane of the sapphire substrate 10.