A semiconductor structure includes a substrate and a CMOS structure. The CMOS structure includes a PMOS structure and a NMOS structure. The PMOS structure includes two first source/drain regions disposed in the substrate, a first gate dielectric disposed partially in the substrate between the first source/drain regions, and a fully silicided gate electrode disposed on the first gate dielectric. The NMOS structure includes two second source/drain regions disposed in the substrate, a second gate dielectric disposed partially in the substrate between the second source/drain regions, and a non-silicided conductive gate electrode disposed on the second gate dielectric.