Semiconductor device to suppress leakage current

A semiconductor device, comprising:

• a semiconductor substrate which has an upper surface and a lower surface and is provided with a drift region of a first conductivity type;
• a buffer region which is provided between the drift region and the lower surface in the semiconductor substrate and has one or more doping concentration peaks having a higher doping concentration than the drift region;
• and
• a lifetime control portion which is provided in the buffer region at a position overlapping a shallowest concentration peak closest to the lower surface among the one or more doping concentration peaks provided in the buffer region, and in which a carrier lifetime shows a local minimum,
• wherein
• the semiconductor substrate has a critical depth position at which an integrated value, which is obtained by integrating doping concentrations from an upper end of the drift region toward the lower surface of the semiconductor substrate, reaches a critical integrated concentration nc of the semiconductor substrate, the critical integrated concentration nc being defined as
• nc=εs×Ec/q
• where εs represents a dielectric constant of a material forming the semiconductor substrate, q represents an elementary charge, and Ec represents a dielectric destruction electric field intensity of the semiconductor substrate, the critical depth position being in the buffer region, and
• a depth position at which the carrier lifetime shows the local minimum in the lifetime control portion is closer to the lower surface than the critical depth position.