Method of manufacturing a thin film device substrate wherein no trench fabrication is required to be applied onto the substrate surface, and a material which is impervious to light can be used, and the substrate can be peeled off quickly. Firstly, a peeling-off film, a silicon oxide film and an amorphous silicon film are formed in succession on a glass substrate, and the amorphous silicon film is irradiated from above to obtain a polycrystalline silicon film. Subsequently, using the polycrystalline silicon film as an active layer, a TFT is formed, and then a plastic substrate is bonded thereon, and finally the glass substrate is peeled off with the peeling-off film, to complete transfer of the TFT. Because the peeling-off film has a gap space, its etching rate is high. Therefore, it is unnecessary to form a trench for supplying an etchant on the surface of the glass substrate.