A semiconductor device fabrication method includes sequentially forming a hard mask layer and a sacrificial layer on a substrate, forming an upper mandrel which includes first to third upper sub-mandrels on the sacrificial layer, the first to third upper sub-mandrels extending in a first direction and being spaced apart from each other in a second direction, a width of the first upper sub-mandrel being smaller than widths of the second and third upper sub-mandrels, forming first spacers on sidewalls of each of the upper sub-mandrels, removing the upper mandrel, etching the sacrificial layer using the first spacers as etching masks to form a lower mandrel that includes a plurality of sub-mandrels, forming second spacers on sidewalls of the lower sub-mandrels, removing the lower mandrel, patterning the hard mask layer and the substrate using the second spacers as etching masks to form first to tenth fins which extend alongside each other in the first direction and are spaced apart from each other in the second direction, removing the first, second, fifth and eighth fins, and forming a first gate electrode that intersects the third, fourth, sixth and seventh fins, and a second gate electrode that intersects the sixth, seventh, ninth and tenth fins while not intersecting the third and fourth fins.