An internal combustion engine igniter semiconductor device is disclosed which is low cost yet secures energy withstand and reverse surge withstand capability. An IGBT includes a clamping diode between a collector electrode and a gate electrode. The IGBT has two n-type buffer layers of differing impurity concentrations between a p+ substrate and an n-type base layer of the IGBT, wherein the total thickness of the two-layer buffer layer is 50 μm or less, and the overall impurity amount is 20×1013 cm−2 or less.