To provide an SOI substrate with an SOI layer that can be put into practical use, even when a substrate with a low allowable temperature limit such as a glass substrate is used, and to provide a semiconductor substrate formed using such an SOI substrate. In order to bond a single-crystalline semiconductor substrate to a base substrate such as a glass substrate, a silicon oxide film formed by CVD with organic silane as a source material is used as a bonding layer, for example. Accordingly, an SOL substrate with a strong bond portion can be formed even when a substrate with an allowable temperature limit of less than or equal to 700° C. such as a glass substrate is used. A semiconductor layer separated from the single-crystalline semiconductor substrate is irradiated with a laser beam so that the surface of the semiconductor layer is planarized and the crystallinity thereof is recovered.