Semiconductor integrated circuit

A semiconductor integrated circuit, comprising:

• a semiconductor substrate having a first conductivity type;
• a first well region having a second conductivity type, which is provided in an upper part of the semiconductor substrate in a high-potential side circuit area defined in the semiconductor substrate;
• a second well region having the first conductivity type, which is provided in an upper part of the first well region and has an impurity concentration higher than an impurity concentration of the semiconductor substrate;
• and
• a first semiconductor region having the second conductivity type, which is provided in a low-potential side circuit area, the low-potential side circuit area being separated from the high-potential side circuit area to be defined in the semiconductor substrate and being operated with potential as a reference, which is lower than reference potential of the high-potential side circuit area,
• wherein a whole semiconductor region having the second conductivity type, which includes the first semiconductor region, has an impurity concentration higher than an impurity concentration of the first well region.