A semiconductor device is provided that includes a substrate, an active region, a pair of gates, a plurality of semiconductor structures and a plurality of pillar structures. The active region is over the substrate. The pair of gates is formed over the active region, and each gate of the pair of gates includes a gate structure and a pair of spacer structures disposed on sidewalls of the gate structure. The plurality of semiconductor structures is arranged between the pair of gates in an alternating arrangement configuration having a first width and a second width. The first width is substantially equal to a width of the gate structure. The plurality of semiconductor structures is separated by the plurality of pillar structures.