Abstract: The present invention provides a semiconductor device, comprising: a semiconductor substrate having a first region and a second region; a first gate structure belong to a PMOS device on the first region; a second gate structure belong to an nMOS device on the second region; a multiple-layer first sidewall spacer on sidewalls of the first gate structure, wherein a layer of the multiple-layer first sidewall spacer adjacent to the first gat structure is an oxide layer; a multiple-layer second sidewall spacer on sidewalls of the second gate structure, wherein a layer of the multiple layers of second sidewall spacer adjacent to the first gat structure is a nitride layer. Application of the present invention may alleviate the oxygen vacancy in a high-k gate dielectric in a pMOS device, and further avoid the problem of EOT growth of an nMOS device during the high-temperature thermal treatment process, and therefore effectively improve the overall performance of the high-k gate dielectric CMOS device.