Patent ID: 8390027

Claim:
A gallium nitride semiconductor device comprising: a silicon semiconductor substrate; a buffer layer provided on a first surface of the silicon semiconductor substrate for crystal structure conversion and/or crystal quality improvement, the buffer layer comprising an aluminum nitride layer on the side of the silicon semiconductor substrate and a gallium nitride layer on the upper side thereof; and an epitaxial gallium nitride semiconductor layer overlying the buffer layer, the silicon semiconductor substrate having a plurality of trenches formed on the side of the substrate opposite the first surface, each trench reaching through the silicon semiconductor substrate and the buffer layer to the epitaxial gallium nitride semiconductor layer, and the inside surface of each of the trenches and the other principal surface of the silicon semiconductor substrate being covered with a metal film wherein the gallium nitride semiconductor device is a vertical semiconductor device in which a first metal film on a first surface and a second metal film on the other principal surface are electrodes for the device.