A semiconductor structure includes a gate structure disposed on a substrate. At least one lightly doped region adjoins the gate structure in the substrate. The at least one lightly doped region has a first conductivity type. A source feature and a drain feature are on opposite sides of the gate structure in the substrate. The source feature and the drain feature have the first conductivity type. The source feature is in the at least one lightly doped region. A bulk pick-up region adjoins the source feature in the at least one lightly doped region. The bulk pick-up region has a second conductivity type.