As a semiconductor device, specifically, a pixel portion included in a semiconductor device is made to have higher precision and higher aperture ratio, it is required to form a smaller wiring in width. In the case of forming a wiring by using an ink-jet method, a dot spreads on a wiring formation surface, and it is difficult to narrow width of a wiring. In the present invention, a photocatalytic substance typified by TiO.sub.2 is formed on a wiring formation surface, and a wiring is formed by utilizing photocatalytic activity of the photocatalytic substance. According to the present invention, a narrower wiring, that is, a smaller wiring in width than a diameter of a dot formed by an ink-jet method can be formed.