According to one embodiment, a nitride semiconductor device includes a first semiconductor, a second semiconductor layer, a third semiconductor layer, a fourth semiconductor layer, a first electrode, a second electrode and a third electrode. The first, second and fourth semiconductor layers include a nitride semiconductor. The second semiconductor layer is provided on the first semiconductor layer, has a band gap not less than that of the first semiconductor layer. The third semiconductor layer is provided on the second semiconductor layer. The third semiconductor layer is GaN. The fourth semiconductor layer is provided on the third semiconductor layer to have an interspace on a part of the third semiconductor layer, has a band gap not less than that of the second semiconductor layer. The first electrode is provided on a portion of the third semiconductor layer. The fourth semiconductor layer is not provided on the portion.