A method for forming a semiconductor device includes providing a substrate and forming conductor patterns and openings on the substrate. Next the openings are filled with a mask layer and upper portions of the conductor patterns are etched to form cavities. Following, a portion of the mask layer is removed to form a trench between two neighboring conductor patterns, wherein the trench exposes the substrate and the sidewalls of the two neighboring conductor patterns. Next, an insulating layer on the cavities and the trench is conformably formed, a second conductive layer is formed on the insulating layer and the trench is filled with the second conductive layer.