A manufacturing method of a semiconductor device at low cost with high reliability, wherein a semiconductor device is manufactured by peeling an element forming layer having a thin film transistor and the like provided over a substrate from the substrate. A metal film is formed on a substrate, plasma treatment is applied thereto to form a metal oxide film on the metal film, an element forming layer is formed on the metal oxide film, an insulating film is formed to cover the element forming layer, an opening is formed in the insulating film and the element forming layer, an etchant is injected through the opening to remove the insulating film and the element forming layer, and the element forming layer is peeled off the substrate. The peeling may be performed by removing the metal film and the metal oxide film partially and then employing a physical means.