A nitride semiconductor element includes a Si substrate; a buffer layer including (a) an AlN layer formed on a primary surface of the Si substrate; and (b) an AlGaN deposit layer formed by laminating multiple AlGaN layers on the AlN layer and having a total thickness ranging from 100 nm to 500 nm; a GaN electron transfer layer formed on the AlGaN deposit layer and having a thickness ranging from 500 nm to 2000 nm provided that the GaN electron transfer layer is thicker than the AlGaN deposit layer; and an AlGaN electron supply layer formed on the GaN electron transfer layer, wherein the AlGaN deposit layer includes an AlGaN layer that is provided closer to the AlN layer and has an Al component that ranges from about 40% to about 60%, and a reference AlGaN layer that has an Al component (%) that is lower than that of the AlGaN layer.