To provide a manufacturing method for a field-effect transistor, such as a thin-film transistor, enabling reductions in the number patterning steps and the number of photomasks and improvements in the throughput and the yield. In the method, an oxide film is formed by processing the surface of a crystalline semiconductor with ozone water or hydrogen peroxide water. Using the oxide film thus formed as an etch stop, a gate electrode, a source electrode, and a drain electrode of the field-effect transistor are simultaneously formed from a same starting film in one patterning step by use of one photomask. After forming the gate electrode, the source electrode, and the drain electrode, heating is performed thereon at 800° C. or higher for a predetermined time. Thereby, the contact resistances between the source electrode and the crystalline semiconductor and between the drain electrode and the crystalline semiconductor are reduced, whereby improving the electrical conductivity.