Patent ID: 8692287

Claim:
A nitride semiconductor device comprising: a stacked foundation layer formed on an AlN buffer layer formed on a silicon substrate, the stacked foundation layer including a plurality of AlN foundation layers and a plurality of GaN foundation layers being alternately stacked with the AlN foundation layers; and a functional layer including: a low-concentration part provided on the stacked foundation layer, the low-concentration part including a nitride semiconductor and having a Si concentration less than 1×10 18 cm −3 ; and a high-concentration part provided on the low-concentration part and having a Si concentration not less than 1×10 18 cm −3 , a substrate-side GaN foundation layer closest to the silicon substrate among the plurality of GaN foundation layers including: a first portion having a Si concentration less than 5×10 18 cm −3 ; a second portion having a Si concentration less than 5×10 18 cm −3 ; and a third portion being provided between the first portion and the second portion, the third portion having a Si concentration not less than 5×10 18 cm −3 and having a thickness smaller than a sum of a thickness of the first portion and a thickness of the second portion.