Nitride semiconductor device, method for manufacturing a nitride semiconductor wafer and a nitride semiconductor layer

A crack was formed on a silicon substrate is less high-quality nitride semiconductor device, to provide a method for manufacturing a nitride semiconductor wafer and a nitride semiconductor layer. According to one embodiment, the stacked foundation layer, a functional layer, a nitride semiconductor device having a are provided. Stacked foundation layer includes a formed on the AlN buffer layer formed on a silicon substrate, a plurality of AlN base layer stacked alternately with a plurality of GaN foundation layer. Functional layer is provided over the stacked foundation layer, and a low-concentration parts of low Si concentration includes a nitride semiconductor, provided on the low-concentration parts, and the high-concentration parts of high Si concentration ,including. Nearest substrate side GaN foundation layer on a silicon substrate among the plurality of GaN foundation layer, a first low Si concentration, and a second low density base portion, a high Si concentration, first, of the second low density base portion having a thin local high concentration base portion than the total thickness. .FIELD 1