A semiconductor device includes a plurality of fins over a substrate. Each fin of the plurality of fins extends in a first direction substantially perpendicular to a bottom surface of the substrate, and each fin of the plurality of fins comprises a first doped region having a first dopant type. The semiconductor device further includes an isolation region over the substrate between a first fin of the plurality of fins and a second fin of the plurality of fins adjacent to the first fin. The semiconductor device further includes a second doped region extends continuously across the isolation region, the second doped region extends into each fin of the plurality of fins, and a dimension of the second doped region in the isolation region in a second direction perpendicular to the first direction is less than a dimension of the at least one isolation region in the second direction.