Manufacturing method of semiconductor device including indium

A manufacturing method of the semiconductor device, the method further comprising:

• forming an electron transit layer, an electron supply layer, and an upper surface layer in order on a substrate by epitaxial growth;
• implanting ions of an impurity element of a first conductivity-type in regions immediately below where a source electrode and a drain electrode are to be formed in the electron supply layer and the upper surface layer;
• forming a heat-protective film on the upper surface layer after the implanting the ions of the impurity element of the first conductivity-type;
• and
• applying heat to activate the implanted ions so that the regions with the implanted ions become first conductivity-type regions;
• removing the heat-protective film and all of the upper surface layer;
• forming the source electrode and the drain electrode on one of the electron supply layer, and the electron transit layer;
• and
• forming a gate electrode on the electron supply layer,
• wherein the electron supply layer is formed of a nitride semiconductor including In,
• wherein the upper surface layer is formed of a material including a nitride of one or more elements selected among B, Al, and Ga.