Semiconductor device

A semiconductor device, comprising:

• a semiconductor substrate of a first conductivity type;
• a first high-voltage insulated-gate field effect transistor formed on a principal surface of the semiconductor substrate;
• a second high-voltage insulated-gate field effect transistor formed on the principal surface of the semiconductor substrate;
• a third high-voltage insulated-gate field effect transistor formed on the principal surface of the semiconductor substrate;
• a first device isolation insulating film that is formed in the semiconductor substrate and isolates the first high-voltage insulated-gate field effect transistor and the second high-voltage insulated-gate field effect transistor from each other;
• a second device isolation insulating film that is formed in the semiconductor substrate and isolates the first high-voltage insulated-gate field effect transistor and the third high-voltage insulated-gate field effect transistor from each other;
• a first impurity diffusion layer of the first conductivity type that is formed below the first device isolation insulating film;
• and
• a second impurity diffusion layer of the first conductivity type that is formed below the second device isolation insulating film,
• wherein the gate electrode of the first high-voltage insulated-gate field effect transistor and the gate electrode of the second high-voltage insulated-gate field effect transistor are connected to each other over the first device isolation insulating film, and
• the impurity concentration of the second impurity diffusion layer is higher than the impurity concentration of the first impurity diffusion layer.