A semiconductor device according to an embodiment includes a silicon carbide layer, an insulating layer, and a region provided between the silicon carbide layer and the insulating layer, the region including a plurality of first atoms of one element from the group consisting of nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Si), at least some of the plurality of first atoms being four-fold coordinated atoms and/or five-fold coordinated atoms.