A semiconductor device includes a substrate having a fin structure extending along a first direction. The fin structure protrudes from a top surface of a trench isolation region and has a first height. A plurality of gate lines including a first gate line and a second gate line extend along a second direction and striding across the fin structure. The first gate line has a discontinuity directly above a gate cut region. The second gate line is disposed in proximity to a dummy fin region, and does not overlap with the dummy fin region. The fin structure has a second height within the dummy fin region, and the second height is smaller than the first height.