Abstract: A method for manufacturing semiconductor device is provided. First, a substrate is provided. Then, a plurality of first gate lines disposed in parallel to each other and a first dummy gate line disposed in a direction perpendicular to the first gate lines are formed on the substrate. There is a first gap between the first dummy gate line and the first gate lines and there is a second gap between every pair of adjacent first gate lines. Thereafter, a second composite layer and a conductive layer are sequentially formed over the substrate. The conductive layer is etched back to form a plurality of second device structures that completely fills the second gaps. Then, the conductive layer in the first gap is removed.