Patent ID: 7944657

Claim:
An electrostatic discharge protection circuit comprising: a first impurity region configured to contain an impurity of a first conductivity type; a second impurity region configured to be formed on a surface of the first impurity region and contain an impurity of the first conductivity type with concentration higher than concentration of the impurity of the first conductivity type in the first impurity region; a first electrode configured to be formed on a surface of the second impurity region and be electrically connected to a signal line; a third impurity region configured to be formed on the surface of the first impurity region and contain an impurity of a second conductivity type different from the first conductivity type; a fourth impurity region configured to be formed on a surface of the third impurity region and contain an impurity of the second conductivity type with concentration higher than concentration of the impurity of the second conductivity type in the third impurity region; a second electrode configured to be formed on a surface of the fourth impurity region and be electrically connected to the signal line; a fifth impurity region configured to be formed in an area adjacent to the third impurity region, of a surface area of the first impurity region, and contain an impurity of the second conductivity type; a sixth impurity region configured to be formed on a surface of the fifth impurity region and contain an impurity of the first conductivity type; a third electrode configured to be formed on a surface of the sixth impurity region and be electrically connected to a reference potential line; a gate insulating film configured to be formed at least on a part of the surface of the first impurity region, between the third impurity region and the fifth impurity region; and a fourth electrode configured to be formed on a surface of the gate insulating film and be electrically connected to the reference potential line when a surge voltage is applied to the signal line.