A method of fabricating a CMOS device having high-k dielectric layer and metal gate electrode is provided. First, an isolation structure is formed in a substrate to define a first-type and a second-type MOS regions; an interfacial layer and a high-k dielectric layer are sequentially formed over the substrate; a first and a second cover layers are respectively formed over a portion of the high-k dielectric layer at the first-type MOS region and another portion of the high-k dielectric layer at the second-type MOS region; afterwards, an in-situ etching step is performed to sequentially etch the first and second cover layers using a first etching solution and to etch both the high-k dielectric layer and the interfacial layer using a second etching solution until the substrate is exposed. Wherein, the second etching solution is a mixed etching solution containing the first etching solution.