Abstract: The present invention relates to a method for producing a semiconductor thin film, in which a single crystalline silicon film is grown on an insulative single crystalline substrate, such as a single crystalline sapphire substrate, by the molecular beam epitaxy method. Silicon molecular beams are irradiated onto the substrate under the conditions wherein a substrate temperature is kept at 700.degree. to 900.degree. C. and an intensity of the molecular beams is kept within a range from 1.times.10.sup.12 atoms/cm.sup.2 .multidot.sec to 1.times.10.sup.13 atoms/cm.sup.2 .multidot.sec to clean a surface of the substrate and then the intensity of the molecular beams is increased to form the single crystalline silicon film. Thus, the substrate can be cleaned without being defected.