A semiconductor device of an embodiment includes: a substrate formed of a single-crystal first semiconductor; a gate insulating film on the substrate; a gate electrode including a layered structure of a semiconductor layer formed of a polycrystalline second semiconductor and a metal semiconductor compound layer formed of a first metal semiconductor compound that is a reaction product of a metal and the second semiconductor; and electrodes formed of a second metal semiconductor compound that is a reaction product of the metal and the first semiconductor, and formed on the substrate with the gate electrode interposed therebetween, and an aggregation temperature of the first metal semiconductor compound on the polycrystalline second semiconductor is lower than an aggregation temperature of the second metal semiconductor compound on the single-crystal first semiconductor, and a cluster-state high carbon concentration region is included in an interface between the semiconductor layer and the metal semiconductor compound layer.