A method of forming a layout of a semiconductor device includes the following steps. First line patterns extend along a first direction in a first area and a second area, but the first line patterns extend along a second direction in a boundary area. Second line patterns extend along a third direction in the first area and the second area, but the second line patterns extend along a fourth direction in the boundary area, so that minimum distances between overlapping areas of the first line patterns and the second line patterns in the boundary area are larger than minimum distances between overlapping areas of the first line patterns and the second line patterns in the first area and the second area. A trimming process is performed to shade the first line patterns and the second line patterns in the boundary area and the second area.