To provide a technical means which is capable of increasing crystallinity and planarity of a single crystal semiconductor layer, crystal defects are reduced in such a manner that a single crystal semiconductor substrate, in which an insulating film is formed on its surface and an embrittlement region is formed in a region at a predetermined depth from the surface, and a supporting substrate are attached to each other with the insulating film interposed therebetween; the single crystal semiconductor substrate is separated in the embrittlement region by a heat treatment; a single crystal semiconductor layer is irradiated with laser light over the supporting substrate with the insulating film interposed therebetween; a surface of the single crystal semiconductor layer is etched; and a plasma treatment is performed on the surface of the single crystal semiconductor layer.