PURPOSE: To obtain a manufacturing method for a thin film transistor wherein a thermal oxide film is made uniform without decreasing the mobility of polycrystalline silicon.

CONSTITUTION: A noncrystalline silicon film 12 as a non-single crystal silicon thin film is formed on an insulative substrate 11. After the noncrystalline silicon film 12 is patterned in a specified island shape, a thermal oxide film 13 is formed by thermal oxidation. Silicon in a channel part is recrystallized as polycrystalline silicon 15 of large grain diameter by heat treatment. A polycrystalline silicon film is formed and patterned as a gate electrode 16, and a source.drain region is formed in a self-alignment manner. A silicon oxide film as an interlayer insulating film 17 is formed, and a contact hole 18 is made in the interlayer insulating film 17. An aluminum electrode 19 is formed and patterned, thereby completing the manufacturing process of an N channel MOS thin film transistor.