Low temperature microwave annealing (MWA) for IC processing is promising. In this study, using microwave annealing for dopant activation and thermal stability of the high-k/metal gate is investigated. Implanted species, such as phosphorus, arsenic, and boron, can also be well-activated and diffusionless in Si after microwave annealing. The flat band voltage shift of metal gate was suppressed due to the low temperature process. The increases in equivalent oxide thickness (EOT) of the MOS devices after dopant activation processing can be eliminated by using low temperature MWA. In addition, the short channel effects in n & pMOSFETs annealed by MWA can be also improved due to the suppression of dopant diffusion and stabilization of EOT.