In a low voltage drive circuit section of a semiconductor integrated circuit, the gate oxide films are approximately 250 ANGSTROM , and a low voltage N-channel IGFET and a low voltage P-channel IGFET are operable at high speed and driven at a low voltage. In a high voltage driven circuit section, the gate oxide films are approximately 1500 ANGSTROM , and a high voltage N-channel IGFET and a high voltage P-channel IGFET are designed to have a high breakdown voltage performance. In a low gate voltage/high voltage drive circuit section, the gate oxide films are approximately 250 ANGSTROM , and a high voltage N-channel IGFET is driven at a low gate voltage and operable at high speed. The high voltage N-channel IGFET of the low gate voltage/high voltage drive circuit section has an offset structure including a drain diffusion layer of low concentration, such that the breakdown voltage of the drain is greatly increased.
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