To provide a semiconductor device manufacturing method capable of forming a gate electrode of a designed shape and size.

A semiconductor device manufacturing method according to a present embodiment comprises: forming laminates 17, 18 in which titanium layers 17a, 18a, aluminum layers 17b, 18b, nickel layers 17c, 18c and gold layers 17d, 18d are respectively laminated in this order on a surface of a semiconductor layer 12 at locations at a distance from each other; heating the laminates at a temperature higher than a melting point of aluminum to form a plurality of metal bodies 17', 18'; concurrently, forming ohmic contacts between the plurality of metal bodies 17', 18' and the semiconductor layer 12; subsequently, thinning the plurality of metal bodies 17', 18' to form a plurality of alloy layers 13a, 14a; forming a drain electrode 13 and a source electrode 14 respectively including the alloy layers 13a, 14a; subsequently, forming an opening 20 in a resist layer 19 between the drain electrode 13 and the source electrode 14; and forming a gate electrode 15 in the opening 20.