The present disclosure provides a semiconductor device with void-free contacts and a method for preparing the semiconductor device. The semiconductor device includes a source/drain structure disposed over a semiconductor substrate, a dielectric layer disposed over the source/drain structure, and a conductive contact penetrating through the dielectric layer and the source/drain structure, wherein the conductive contact comprises a conductive layer and a barrier layer covering a sidewall and a bottom surface of the conductive layer. A first thickness of the harrier layer on the sidewall of the conductive layer is less than a second thickness of the barrier layer under the bottom surface of the conductive layer.