A substrate for forming a semiconductor substrate, for the purpose of forming a semiconductor substrate in which a plurality of single crystal semiconductor films are disposed on a base substrate, characterized in that
- a plurality of stacked substrates, in which a first insulating film, a single crystal semiconductor film, a second insulating film, and a support substrate having a fragile layer formed by ion irradiation and being made from a single crystal semiconductor material are stacked sequentially, are bonded to a base substrate in such a way that the first insulating film is located on a side close to the base substrate, and
- a film thickness of the second insulating film in a stacked substrate is less than or equal to one-third a sum of the film thicknesses of the first insulating film and the single crystal semiconductor film.