In the present application, is disclosed a method of manufacturing a flexible semiconductor device having an excellent reliability and tolerance to the loading of external pressure. The method includes the steps of: forming a separation layer over a substrate having an insulating surface; forming an element layer including a semiconductor element comprising a non-single crystal semiconductor layer, over the separation layer; forming an organic resin layer over the element layer; providing a fibrous body formed of an organic compound or an inorganic compound on the organic resin layer; heating the organic resin layer; and separating the element layer from the separation layer. This method allows the formation of a flexible semiconductor device having a sealing layer in which the fibrous body is impregnated with the organic resin.