Abstract: There is disclosed a method of manufacturing a contact plug in a semiconductor device using selective epitaxial growth of silicon (SEG) process. The method includes forming a nitride film at a predetermined in a semiconductor substrate region except for the region in which a contact plug will be formed, forming an USG film on the entire surface of the substrate in which the nitride film is formed by chemical enhanced vapor deposition method or a plasma method, etching the USG film by reactive ion etch method to expose the surface of silicon in the structure, and forming a contact plug by performing in-situ process while performing selective epitaxial growth method for the silicon film exposed through the contact hole in the structure.