PROBLEM TO BE SOLVED: To provide an oxide semiconductor film which can improve reliability of a thin film transistor.SOLUTION: Provided is an oxide semiconductor thin film in which molecular weight of water desorbed within a temperature ranged of not less than 200°C and not more than 600°C is not lower than 3×10cm; and molecular weight of water desorbed within a temperature range of not less than 200°C and less than 400°C is not greater than 1×10cm; and molecular weight of water desorbed within a temperature range of not less than 400°C and not more than 600°C is not lower than 1×10cmin a thermal desorption method.