A layout design system for designing a semiconductor device includes a processor, a storage module storing an intermediate design, and a correction module used by the processor to correct the intermediate design. The intermediate design includes an active region and dummy designs on the active region. Each dummy design includes a dummy structure and dummy spacers disposed at opposite sides of the dummy structure. The correction module is configured to alter widths of regions of at least some of the dummy designs. The corrected design is used to produce a semiconductor device having an active fin, a hard mask layer disposed on the active fin, a gate structure crossing the over the hard mask layer, and a spacer disposed on at least one side of the gate structure. The hard mask layer, and the active fin, are provided with widths that vary due to the dummy designs.