Method for manufacturing semiconductor device

A method for manufacturing a semiconductor device having a source electrode, a drain electrode, and a gate electrode provided between the source electrode and the drain electrode, the method comprising steps of:

• forming a protective film on a semiconductor substrate;
• forming a resist film on the protective film such that the resist film includes a region where the resist film becomes thicker from the drain electrode to the source electrode, the region being provided between the source electrode and the drain electrode;
• forming a first opening in the resist film by irradiating the resist film in the region with an electron beam and developing the resist film;
• forming a second opening that exposes an upper surface of the semiconductor substrate by removing the protective film using the resist film in which the first opening is formed as a mask;
• forming a third opening in the resist film by further developing the resist film after forming the second opening, the third opening being formed by expanding the first opening toward the drain electrode;
• and
• forming the gate electrode in the second opening and the third opening.