A method of manufacturing a reverse blocking insulated gate bipolar transistor to form an isolation layer for bending and extending a pn junction, which exhibits a high reverse withstand voltage, to the front surface side. This ensures a high withstand voltage in the reversed direction and reduces leakage current in the reversely biased condition. Formation of a tapered groove by an anisotropic alkali etching process is conducted, resulting in a semiconductor substrate left with a thickness of at least 60 μm between one principal surface and the bottom surface of the tapered groove formed from the other principal surface.