In the method for manufacturing a semiconductor device, a resist film is formed on a substrate and is processed to be provided with openings to form a first resist pattern. Additive-containing layers containing an additive that changes a state of the resist film to a soluble state for a developer are formed so as to cover the first resist pattern. A first resin film having a nature of changing to a soluble state for the developer by containing the additive is formed in the openings of the first resist pattern. The additive is diffused into the first resist pattern and the first resin film to form first and second additive-diffusing portions which can be solved in the developer. The first and second additive-diffusing portions are removed by the developer to form second resist pattern made of remaining portions in the first resist pattern and the first resin film.