A stack package and a method of manufacturing the stack package are provided. The method includes: attaching a first semiconductor device onto a first surface of a first package substrate; attaching a molding resin material layer onto a first surface of a second package substrate; arranging the first surface of the first package substrate and the first surface of the second package substrate to face each other; compressing the first package substrate and the second package substrate while reflowing the molding resin material layer; and hardening the reflowed molding resin material layer.