In a semiconductor device having a vertical semiconductor element configured to pass an electric current between an upper electrode and a lower electrode, a field stop layer includes a phosphorus/arsenic layer doped with phosphorus or arsenic and a proton layer doped with proton. The phosphorus/arsenic layer is formed from a back side of a semiconductor substrate to a predetermined depth. The proton layer is deeper than the phosphorus/arsenic layer. An impurity concentration of the proton layer peaks inside the phosphorus/arsenic layer and gradually, continuously decreases at a depth greater than the phosphorus/arsenic layer.