According to one embodiment, a semiconductor device includes an n-type semiconductor layer containing diamond, a first electrode including a first portion, an intermediate layer, and a p-type semiconductor layer containing diamond. The intermediate layer contains at least any of a carbide, graphite, graphene, and amorphous carbon. The carbide contains at least any of Ti, Si, Al, W, Ni, Cr, Ca, Li, Ru, Mo, Zr, Sr, Co, Rb, K, Cu, and Na. The intermediate layer includes a first region provided between the first portion and the n-type semiconductor layer, and a second region provided around the first region when projected on a plane perpendicular to a direction from the n-type semiconductor layer to the first electrode. The second region does not overlap the first portion, and is continuous with the first region.