Semiconductor device and method of manufacturing semiconductor device

A semiconductor device comprising:

• a substrate;
• a plurality of pairs of semiconductor layers on the substrate;
• and
• a gate electrode, a drain electrode, and a source electrode provided on the plurality of pairs of semiconductor layers, wherein
• each of the plurality of pairs of semiconductor layers includes a channel layer made with GaN and a barrier layer provided in contact with an upper surface of the channel layer and made with AlxGa1-xN,
• a carbon concentration of the channel layer included in an uppermost pair of semiconductor layers among the plurality of pairs of semiconductor layers is lower than an average value of carbon concentration of the channel layers included in the pairs of semiconductor layers other than the uppermost pair of semiconductor layers, and
• the uppermost pair of semiconductor layers is an uppermost pair of channel and barrier layers in the semiconductor device.