Semiconductor device

A semiconductor device comprising:

• a semiconductor layer having a first plane and a second plane opposite to the first plane, the semiconductor layer including a first-conductivity-type first semiconductor region, a second-conductivity-type second semiconductor region, a first-conductivity-type third semiconductor region, and a second-conductivity-type fourth semiconductor region, the second semiconductor region being provided between the first semiconductor region and the first plane, the third semiconductor region being provided between the second semiconductor region and the first plane, the third semiconductor region having a lower first-conductivity-type impurity concentration than the first semiconductor region, the fourth semiconductor region being provided between the third semiconductor region and the first plane, the fourth semiconductor region having a higher second-conductivity-type impurity concentration than the second semiconductor region;
• a first electrode provided on a side of the first plane of the semiconductor layer, the first electrode being electrically connected to the third semiconductor region and the fourth semiconductor region;
• and
• a second electrode provided on a side of the second plane of the semiconductor layer, the second electrode being electrically connected to the first semiconductor region, the second electrode not being electrically connected to the second semiconductor region.