A method for fabricating a semiconductor device includes the steps of forming a metal gate on a substrate, a contact etch stop layer (CESL) adjacent to the metal gate, and an interlayer dielectric (ILD) layer around the gate structure, performing a first etching process to remove the ILD layer, performing a second etching process to remove the CESL for forming a first contact hole, and then forming a first contact plug in the first contact hole. Preferably, a width of the first contact plug adjacent to the CESL is less than a width of the first contact plug under the CESL.