An N-type buried diffusion layer as a portion of the collector region of a bipolar transistor and an N-type buried diffusion layer of a memory cell region are simultaneously formed, and the buried diffusion layer of the memory cell region serves as a potential groove for electrons. The threshold voltage of a MOS transistor in the memory cell region is higher than the threshold voltage of a MOS transistor in a peripheral circuit region, preventing an increase in the standby current in the memory cell region. This increases the soft error resistance of the memory cell and prevents a decrease in the operating speed and an increase in the consumption power.