A method for forming a semiconductor device includes forming a partition line pattern and a partition pad pattern connected to an end part of the partition line pattern over the semiconductor substrate. Spacer insulation layers are formed at sidewalls of the partition line pattern and the partition pad pattern. A gap-filling layer is formed between the spacer insulation layers. A first cutting mask pattern is formed to expose a connecting part between the partition line pattern and the partition pad pattern. The partition line pattern and the gap-filling layer adjacent to the spacer insulation layer are removed using the first cutting mask pattern as a mask. A second cutting mask pattern including a first pattern and a second pattern are formed. The spacer insulation layer is removed using the second cutting mask pattern as a mask to form a gate trench in the substrate.