A method of forming a metal line of a semiconductor memory device is disclosed. An interlayer insulating layer, an etch-stop layer, a trench oxide layer, a hard mask layer and a photoresist layer are laminated over a semiconductor substrate in which a contact is formed. An exposure process is performed to form a photoresist pattern. The hard mask layer is partially etched by an etch process that employs the photoresist pattern. An etch process using the hard mask layer as an etch mask is performed to partially etch the trench oxide layer, the etch-stop layer and the interlayer insulating layer, thereby forming damascene trenches. Metal material is formed on the entire surface including the trenches. A chemical mechanical polishing process is then performed to expose the etch-stop layer, thereby forming a metal line.