When a single crystal semiconductor layer is bonded to a base substrate, a silicon oxide film is preferably used for one or both of the base substrate and a single crystal semiconductor substrate. According to this structure, an SOI layer having a strong bonding strength in a bonding portion can be obtained even when a substrate having an upper temperature limit of 700° C. or lower such as a glass substrate is used. In addition, a single crystal semiconductor substrate from which the single crystal semiconductor layer has been separated is reprocessed in such a manner that the single crystal semiconductor substrate is irradiated with laser light from the separation surface side of the single crystal semiconductor substrate, to melt the surface of the single crystal semiconductor substrate during the melting time per area of 0.5 microseconds to 1 millisecond. Then, the reprocessed single crystal semiconductor substrate is reused.