According to one embodiment, a semiconductor device includes a first semiconductor region including a first compound including silicon and carbon, and a second semiconductor region including a second compound including silicon and carbon. The first semiconductor region includes first to third regions contacting the second semiconductor region. The third region is positioned between the first region and the second region. The first region and the second region include germanium. The third region does not include germanium, or a concentration of germanium in the third region is lower than a concentration of germanium in the first region and lower than a concentration of germanium in the second region.