A method of manufacturing a semiconductor device, including forming a molding layer; forming a damascene mask layer and mask layer on the molding layer; forming a mask layer pattern by etching the mask layer; forming a damascene pattern by partially etching the damascene mask layer; forming a damascene mask layer on the mask layer pattern to bury the damascene pattern; forming a damascene pattern partially overlapping the damascene pattern by etching the damascene mask layer and the mask layer pattern; connecting the damascene pattern and the damascene pattern by removing a portion of the mask layer pattern exposed by the damascene pattern; forming a damascene mask layer on the damascene mask layer to bury the damascene pattern; and forming a trench under the damascene patterns by etching the damascene mask layers and the molding layer using remaining portions of the mask layer pattern.