Semiconductor device having electrostatic discharge protection circuit

A semiconductor device manufactured by a SOI-CMOS process, comprising:

• an power supply terminal, an output terminal and a ground terminal;
• an insulator;
• a first electrostatic discharge protection circuit formed on the insulator, the first electrostatic discharge protection circuit including a first lightly doped diffusion layer of a first conductivity type, two first highly doped diffusion layers of the first conductivity type, and a first gate electrode formed on the first lightly doped layer, the first lightly doped diffusion layer being sandwiched by the first highly doped layers, one of the first highly doped layers being connected to the output terminal and the first gate electrode being connected to the power supply terminal, and the first electrostatic discharge protection circuit serving as a resistor or an insulator according to the polarity of an electrostatic surge applied to the output terminal;
• and
• a first conductivity type output transistor having a gate electrode, a source and a drain, the source being connected to the ground terminal;
• wherein the first electrostatic discharge protection circuit and the first conductivity type output transistor are connected to each other in series between the output terminal and the ground terminal.