Disclosed is a manufacturing method of a high electron mobility transistor. The method includes: forming a source electrode and a drain electrode on a substrate; forming a first insulating film having a first opening on an entire surface of the substrate, the first opening exposing a part of the substrate; forming a second insulating film having a second opening within the first opening, the second opening exposing a part of the substrate; forming a third insulating film having a third opening within the second opening, the third opening exposing a part of the substrate; etching a part of the first insulating film, the second insulating film and the third insulating film so as to expose the source electrode and the drain electrode; and forming a T-gate electrode on a support structure including the first insulating film, the second insulating film and the third insulating film.