Semiconductor device

A semiconductor device comprising:

• a semiconductor substrate of a first conductivity type having a first main surface and a second main surface on a side opposite to the first main surface;
• a first semiconductor region of a second conductivity type formed on a first main surface side of the semiconductor substrate;
• a second semiconductor region of the second conductivity type formed so as to be enclosed by the first semiconductor region on the first main surface side of the semiconductor substrate;
• third and fourth semiconductor regions of the first conductivity type formed away from each other so as to be enclosed by the second semiconductor region on the first main surface side of the semiconductor substrate;
• a fifth semiconductor region of the second conductivity type formed on a second main surface side of the semiconductor substrate;
• a sixth semiconductor region of the first conductivity type formed so as to be enclosed by the fifth semiconductor region on the second main surface side of the semiconductor substrate;
• a substrate region of the first conductivity type composed of a part of the semiconductor substrate and interposed between the first semiconductor region and the fifth semiconductor region;
• a seventh semiconductor region of the second conductivity type interposed between the fifth semiconductor region and the substrate region;
• a first electrode formed on the first main surface of the semiconductor substrate so as to be in contact with the second and third semiconductor regions;
• a second electrode formed on the first main surface of the semiconductor substrate so as to be in contact with the second and fourth semiconductor regions;
• and
• a third electrode formed on the second main surface of the semiconductor substrate so as to be in contact with the fifth and sixth semiconductor regions,
• wherein a first thyristor is formed of the fifth semiconductor region, the seventh semiconductor region, the substrate region, the first semiconductor region, the second semiconductor region and the third semiconductor region between the third electrode and the first electrode,
• a second thyristor is formed of the second semiconductor region, the first semiconductor region, the substrate region, the seventh semiconductor region, the fifth semiconductor region and the sixth semiconductor region between the first electrode and the third electrode,
• directions of a current flowing between the first electrode and the third electrode are opposite to each other in the first thyristor and the second thyristor,
• impurity concentrations of the second and fifth semiconductor regions are higher than impurity concentrations of the first and seventh semiconductor regions,
• impurity concentrations of the third, fourth and sixth semiconductor regions are higher than an impurity concentration of the substrate region, and
• distances from bottom surfaces of the third and fourth semiconductor regions of the first conductivity type to a bottom surface of the second semiconductor region of the second conductivity type are larger than a distance from a bottom surface of the second semiconductor region of the second conductivity type to a bottom surface of the first semiconductor region of the second conductivity type.