Nitride semiconductor device

A nitride semiconductor device, comprising:

• a substrate;
• a first nitride semiconductor layer above the substrate, the first nitride semiconductor layer being of an n-type;
• a second nitride semiconductor layer above the first nitride semiconductor layer, the second nitride semiconductor layer being of a p-type;
• a gate electrode covering a first opening which penetrates through the second nitride semiconductor layer to the first nitride semiconductor layer;
• and
• a drain electrode on a side of the substrate opposite from a side of the substrate on which the first nitride semiconductor layer is located,
• wherein the gate electrode includes
• a third nitride semiconductor layer and a metal layer including a metal material, in the stated order from a side on which the substrate is located, and
• wherein a bottom face of the third nitride semiconductor layer is closer to the drain electrode than a bottom face of the second nitride semiconductor layer is.