A method of forming single-crystal semiconductor films, in which a single-crystal semiconductor substrate having a crystal axis transferred from a single-crystal semiconductor substrate is formed on an insulator layer via a seed hole which goes through the insulator layer which is formed on the single-crystal semiconductor substrate, comprises the steps of: forming a non-single-crystal semiconductor substrate connected to a single-crystal semiconductor substrate via a seed hole on an insulator layer; irradiating a compound beam which includes a first energy beam having a power density which is capable of melting a non-single-crystal semiconductor film and a second energy beam having a power density which is not capable of melting the non-single-crystal semiconductor film but capable of softening the insulator layer positioned below the non-single-crystal semiconductor film; and epitaxially growing the single-crystal semiconductor film in such a way that the non-single-crystal semiconductor film is melted and then solidified again by scanning the surface of the non-single-crystal semiconductor film with the compound beam, starting from the seed hole, in such a manner that the first energy beam is irradiated first and the second energy beam is irradiated second.