Manufacturing method of semiconductor device that includes forming plural nitride semiconductor layers of identical material

A manufacturing method of a semiconductor device, comprising:

• forming a first nitride semiconductor layer on a substrate using a first temperature;
• decreasing a substrate temperature to a second temperature lower than the first temperature, after the forming the first nitride semiconductor layer;
• forming a second nitride semiconductor layer on the first nitride semiconductor layer using the second temperature, the second nitride semiconductor layer formed of a material identical to a material of the first nitride semiconductor layer;
• increasing the substrate temperature to a third temperature higher than the first temperature, after the forming the second nitride semiconductor layer;
• and
• forming a third nitride semiconductor layer on the second nitride semiconductor layer using the third temperature, the third nitride semiconductor layer formed of a material identical to the material of the first nitride semiconductor layer.