The present invention provides a semiconductor device fabrication method capable of reducing the thermal load on the substrate. The present invention also provides a semiconductor device fabrication method capable of improving the characteristics of a semiconductor element. The semiconductor device fabrication method according to the present invention comprises a step of thermally processing a semiconductor layer that is deposited on a substrate by using, as a heat source, the flame of a gas burner that uses a mixed gas of hydrogen and oxygen as fuel. As a result of thermal processing, the semiconductor layer is re-crystallized and an oxide film is formed on the surface of the semiconductor layer. The oxide film can be used as a gate insulation film and a capacitive insulation film.