The present disclosure provides a semiconductor device that includes a semiconductor substrate, a gate structure disposed on a surface of the substrate, and strained structures disposed in the substrate at either side of the gate structure and formed of a semiconductor material different from the semiconductor substrate. Each strained structure has a cross-sectional profile that includes a first portion that extends from the surface of substrate and a second portion that tapers from the first portion at an angle ranging from about 50° to about 70°. The angle is measured with respect to an axis parallel to the surface of the substrate.