Patent ID: 7569870

Claim:
A semiconductor device comprising: a substrate of silicon or a silicon compound; a buffer layer on one of opposite major surfaces of the substrate, the buffer layer having a first sublayer of a nitride semiconductor containing aluminum in a first proportion, a second sublayer of a nitride semiconductor containing aluminum in a second proportion that is either zero or less than the first proportion, and a third sublayer interposed between the first and the second sublayer and made from a substance capable of restricting the generation of two-dimensional electron gas; a main semiconductor region having at least one nitride semiconductor layer formed on the buffer layer for providing a field-effect transistor, and having a major surface; a source electrode on the major surface of the main semiconductor region; a drain electrode on the major surface of the main semiconductor region spaced from the source electrode; and a gate electrode interposed between the source electrode and the drain electrode on the major surface of the main semiconductor region.