Nitride semiconductor device

A nitride semiconductor device comprising:

• a substrate;
• a first semiconductor layer of a first conductivity type disposed above the substrate;
• a second semiconductor layer of a second conductivity type disposed above the first semiconductor layer;
• a third semiconductor layer that is disposed above the second semiconductor layer and has a resistance higher than a resistance of the second semiconductor layer;
• a fourth semiconductor layer of the second conductivity type disposed above the third semiconductor layer;
• a fifth semiconductor layer including a channel region of the first conductivity type, a portion of the fifth semiconductor layer being disposed along an inner surface of a first opening and an other portion of the fifth semiconductor layer being disposed above the fourth semiconductor layer, the first opening penetrating through the fourth semiconductor layer, the third semiconductor layer, and the second semiconductor layer and reaching the first semiconductor layer;
• a sixth semiconductor layer of the second conductivity type disposed above the fifth semiconductor layer;
• a gate electrode disposed above the sixth semiconductor layer;
• a source electrode spaced from the gate electrode;
• and
• a drain electrode disposed below a bottom surface of the substrate.