A semiconductor structure includes a semiconductor substrate; a gate stack on the semiconductor substrate; an epitaxial region having at least a portion in the semiconductor substrate and adjacent to the gate stack, wherein the epitaxial region comprises an impurity of a first conductivity type; a first portion of the semiconductor substrate adjoining the epitaxial region, wherein the first portion of the semiconductor substrate is of the first conductivity type; and a second portion of the semiconductor substrate adjoining the first portion. The second portion of the semiconductor substrate is of a second conductivity type opposite the first conductivity type. A silicide region is formed on the epitaxial region and the first and the second portions of the semiconductor substrate.