A method includes: forming a photoresist pattern to form each of a semiconductor element mounting section on which a semiconductor element is mounted, semiconductor element electrode connection terminals for connection with electrodes of the semiconductor element, and a first outer frame section on a first surface of a metal plate; forming a photoresist pattern to form each of external connection terminals, a second outer frame section, and grooves in at least a part of the second outer frame section on a second surface of the metal plate; etching a metal plate exposing section, in which the metal plate of the second surface is exposed, to form holes that do not pass through the metal plate exposing section and grooves that run from an inside to an outside of the second outer frame section; coating a pre-mold resin on the holes and the grooves, and heating the pre-mold resin under pressure using a flat-bed press to form a resin layer; and etching the first surface to form the semiconductor element mounting section, the semiconductor element electrode connection terminals electrically connected with the external connection terminals, and the first outer frame section.