An SOI substrate is manufactured by forming an embrittled layer in a bond substrate by increasing the dose of hydrogen ions in the formation of the embrittled layer to a value more than the dose of hydrogen ions of the lower limit for separation of the bond substrate, separating the bond substrate attached to the base substrate, forming an SOI substrate in which a single crystal semiconductor film is formed over the base substrate, and irradiating a surface of the single crystal semiconductor film with laser light.