The invention provides a method of producing a semiconductor device conforming to plural supply voltage specifications without increasing the chip size and the production cost, while the device achieves a high-speed performance. The method includes plural processes for forming plural types of MOS transistors supplied with different power supply voltages in correspondence with external power supply voltages, which are comprised of a first process common to the plural types of MOS transistors, a second process following the first process, which is different by each of the plural types of MOS transistors, and a third process following the second process, which is common to the plural types of MOS transistors.