A method for manufacturing a semiconductor device comprises: growing a carbon nano tube on a semiconductor substrate; forming an insulating film in the inside and the outside of the carbon nano tube; and forming a graphene on the surface of the insulating film, thereby securing a channel region corresponding to a region extended by the carbon nano tube to prevent a short channel effect. As a result, channel resistance is reduced to facilitate the manufacturing of the device that can be operated at a high speed. The carbon nano tube is applied to a semiconductor device of less than 30 nm so that a micro-sized semiconductor device can be manufactured regardless of limitation of exposure light sources.