An object is to provide a method for manufacturing a semiconductor device which suppresses an influence on a semiconductor element due to entry of an impurity element, moisture, or the like from outside even in the case of thinning or removing a substrate after forming a semiconductor element over the substrate. A feature is to form an insulating film functioning as a protective film on at least one side of the substrate by performing surface treatment on the substrate, to form a semiconductor element such as a thin film transistor over the insulating film, and to thin the substrate. As the surface treatment, addition of an impurity element or plasma treatment is performed on the substrate. As a means for thinning the substrate, the substrate can be partially removed by performing grinding treatment, polishing treatment, or the like on the other side of the substrate.