Semiconductor device

A semiconductor device, comprising:

• a substrate;
• a channel layer which is constituted of a single layer of a nitride semiconductor disposed over the substrate and having a first band gap;
• a first barrier layer which is a nitride semiconductor disposed on and in contact with a selected part of an upper surface of the channel layer and having a second band gap larger than the first band gap of the channel layer;
• a gate layer which is a nitride semiconductor containing a p-type impurity, the gate layer is disposed on and in contact with a selected part of an upper surface of the first barrier layer;
• a second barrier layer which is a nitride semiconductor disposed in contact with both the channel layer and the first barrier layer, in an area where the gate layer is not disposed, the second barrier layer having a third band gap which is larger than the first band gap of the channel layer, and having a thickness and a band gap that are independently set with respect to the first barrier layer, the second barrier layer being a different layer distinguished from the first barrier layer;
• a gate electrode which is disposed on the gate layer;
• and
• a source electrode and a drain electrode which are spaced apart from the gate layer and disposed on the second barrier layer, wherein:
• a cross sectional shape along a source-to-drain direction of the gate layer is a forward tapered shape having a top smaller than a bottom,
• a lower surface of the second barrier layer is located lower than a lower surface of the first barrier layer, and
• the channel layer is continuous from a portion below the source electrode to a portion below the drain electrode,
• the first barrier layer is disposed only in an area from below the gate layer to a side of the source electrode in a plan view, and
• the second barrier layer in the area is disposed on the first barrier layer.