Semiconductor device

A semiconductor device, comprising:

• a first nitride semiconductor layer that is made over a substrate;
• a second nitride semiconductor layer that is formed on the first nitride semiconductor layer;
• a third nitride semiconductor layer that is formed on the second nitride semiconductor layer;
• a fourth nitride semiconductor layer that is formed on the third nitride semiconductor layer;
• a gate electrode that is arranged above the fourth nitride semiconductor layer through the fifth nitride semiconductor layer;
• a first electrode and a second electrode that are formed above the fourth nitride semiconductor layer on both sides of the gate electrode;
• a first connection portion that connects the first electrode to the first nitride semiconductor layer;
• a second connection portion that connects the second electrode to the second nitride semiconductor layer;
• and
• an insulating film that is formed between the first connection portion and the second nitride semiconductor layer,
• wherein an electron affinity of the fourth nitride semiconductor layer is smaller than an electron affinity of the third nitride semiconductor layer,
• wherein an electron affinity of the fifth nitride semiconductor layer is larger than an electron affinity of the fourth nitride semiconductor layer,
• wherein the first nitride semiconductor layer contains impurities of a first conductivity type,
• wherein the second nitride semiconductor layer contains impurities of a second conductivity type that is a conductivity type opposite to the first conductivity type,
• wherein the substrate has a first region and a second region,
• wherein the gate electrode, the first electrode, and the second electrode are formed in the first region,
• wherein the second region is a device isolation region formed in the fourth nitride semiconductor layer and the third nitride semiconductor layer,
• wherein the first connection portion is arranged within a first through-hole that penetrates through the device isolation region and the second nitride semiconductor layer, and reaches the first nitride semiconductor layer,
• wherein the insulating film is arranged between a side wall of the first through-hole and the first connection portion, and
• wherein the second connection portion is arranged within a second through-hole that penetrates through the device isolation region, and reaches the second nitride semiconductor layer.