A semiconductor device according to an embodiment includes a substrate. A transistor includes a source layer and a drain layer that are provided in a surface region of the substrate and contain impurities. A gate dielectric film is provided on the substrate between the source layer and the drain layer. A gate electrode is provided on the gate dielectric film. A first epitaxial layer is provided on the source layer or the drain layer. A second epitaxial layer is provided on the first epitaxial layer and contains both the impurities and carbon. A contact plug is provided on the second epitaxial layer. A memory cell array is provided above the transistor.