PURPOSE: To lessen a CMOS transistor of low/high voltage in number of manufacturing processes.

CONSTITUTION: After a gate electrode 6 of polysilicon is formed, a process where phosphorus ions are implanted into an N-channel transistor region 22 of high voltage and a P-channel transistor transistor region 21 of low voltage, a second process where boron ions are implanted into a P-channel transistor region 23 of high voltage and an N-channel transistor of low voltage, and a press-in process are provided, and the control of a transistor of low voltage in threshold voltage and the formation of an electrical field relaxation low concentration region of a transistor of high voltage are carried out through an ion implantation process and a press-in process.