A CMOS device with transistors having different gate dielectric materials and a method of manufacture thereof. An aluminum-based material is used as a gate dielectric material of a PMOS device, and a hafnium-based material is used as a gate dielectric material of an NMOS device. A thin layer of silicon a few monolayers or a sub-monolayer thick is formed over the gate dielectric materials, before forming the gates. The thin layer of silicon bonds with the gate dielectric material and pins the work function of the transistors. A gate material that may comprise a metal in one embodiment is deposited over the thin layer of silicon. A CMOS device having a symmetric Vt for the PMOS and NMOS FETs is formed.