According to one embodiment, a nitride semiconductor device includes semiconductor stacked layers provided on a substrate and including a nitride semiconductor; a source electrode and a drain electrode provided on the layers and being in contact with the layers; and a gate electrode provided on the layers and provided between the source electrode and the drain electrode. The layers have a first barrier layer, a second barrier layer, and a carrier running layer interposed between the first barrier layer and the second barrier layer. The second barrier layer and the carrier running layer are removed in a region in which the source electrode on the layers is provided. A part of the source electrode is in contact with the first barrier layer. And another part of the source electrode other than the part of the source electrode is in contact with the second barrier layer.