A method of manufacturing a semiconductor device includes: forming a metal film containing Al on a surface of a substrate product including a substrate and a nitride semiconductor layer on the substrate, the metal film covering a via hole forming predetermined region, and the surface of the substrate product being located on the nitride semiconductor layer side, forming an etching mask having an opening for exposing the via hole forming predetermined region on a back surface of the substrate product, the back surface of the substrate product being located on the substrate side, and forming a via hole in the substrate product by reactive ion etching, the via hole reaching the surface from the back surface and exposing the metal film. In the forming of the via hole, a reaction gas containing fluorine is used during a period at least including a termination of etching.