A method of fabricating a gate cap layer includes providing a substrate with an interlayer dielectric disposed thereon, wherein a recess is disposed in the interlayer dielectric and a metal gate fills in a lower portion of the recess. Later, a cap material layer is formed to cover the interlayer dielectric and fill in an upper portion of the recess. After that, a first sacrifice layer and a second sacrifice layer are formed in sequence to cover the cap material layer. The first sacrifice layer has a composition different from a composition of the cap material layer. The second sacrifice layer has a composition the same as the composition of the cap material layer. Next, a chemical mechanical polishing process is preformed to remove the second sacrifice layer, the first sacrifice layer and the cap material layer above a top surface of the interlayer dielectric.