The present disclosure provides a semiconductor device that includes a semiconductor substrate having a first region and a second region, a pMOS transistor formed over the first region and an nMOS formed over the second region. The pMOS transistor has a gate structure that includes: an interfacial layer formed over the substrate; a AlOx layer formed over the interfacial layer; and a metal layer including Mo or W formed over the AlOx layer. The nMOS transistor has a gate structure that includes: the interfacial layer formed over the substrate; a DyOx layer formed over the interfacial layer; and the metal layer including Mo or W formed over the DyOx layer.