Patent ID: 8247796

Claim:
A semiconductor device comprising: a substrate; an AlN layer being provided on the substrate; a superlattice buffer layer that is formed directly on the AlN layer on the substrate and is composed of first Al x Ga 1-x N layers and second Al x Ga 1-x N layers having an Al composition greater than that of the first Al x Ga 1-x N layers, the first and second Al x Ga 1-x N layers being alternately stacked one by one, both the Al compositions of the first and second Al x Ga 1-x N layers being greater than 0.3, a difference in Al composition between the first and second Al x Ga 1-x N layers being greater than 0 and smaller than 0.6, and a GaN-based semiconductor provided on the superlattice buffer layer, wherein the GaN-based semiconductor layer has a field effect transistor.