Nitride semiconductor apparatus and manufacturing method thereof

A nitride semiconductor apparatus, comprising:

• a substrate;
• a first nitride semiconductor layer above the substrate, wherein the first nitride semiconductor layer constitutes an electron transit layer;
• a second nitride semiconductor layer on the first nitride semiconductor layer, wherein the second nitride semiconductor layer constitutes an electron supply layer;
• a nitride semiconductor gate layer on the second nitride semiconductor layer, wherein the nitride semiconductor gate layer includes a ridge portion and an acceptor-type impurity;
• a gate electrode on the ridge portion;
• a source electrode that includes:
• a first portion in contact with the second nitride semiconductor layer, and
• a second portion above the gate electrode;
• a drain electrode opposite to the source electrode on the second nitride semiconductor layer, wherein the ridge portion is between the first portion of the source electrode and the drain electrode;
• and
• a strip-shaped insulator between the substrate and a surface layer portion of the first nitride semiconductor layer, wherein
• the strip-shaped insulator extends along a length direction of the ridge portion in a plan view,
• the strip-shaped insulator is below the gate electrode, and
• the strip-shaped insulator has a width greater than twice a width of a bottom surface of the gate electrode.