In the present invention, (Ti.sub.1-xA.sub.x)N [in which A is at least one kind of metal selected from the group consisting of Al, Ga, and In] is used as a metal nitride layer, so that a Group III nitride compound semiconductor layer is formed on the metal nitride layer. When a Ti layer is formed between the metal nitride layer having a sufficient thickness and a substrate and the titanium layer is removed, a Group III nitride compound semiconductor device using metal nitride as a substrate can be obtained.