An insulated gate bipolar transistor has a P-type collector region containing a P-type impurity such as boron. A relatively thin N-type buffer region containing arsenic in a relatively high concentration is formed on the collector region via an anti-diffusion region. The anti-diffusion region is provided in such a way that its thickness is the same as or slightly smaller than the distance over which the P-type impurity is diffused from the collector region toward the buffer region in a device fabrication process.