A semiconductor structure and method that is capable of generating a local mechanical gate stress for channel mobility modification are provided. The semiconductor structure includes at least one NFET and at least one PFET on a surface of a semiconductor substrate. The at least one NFET has a gate stack structure comprising a gate dielectric, a first gate electrode layer, a barrier layer, a Si-containing second gate electrode layer and a compressive metal, and the at least one PFET has a gate stack structure comprising a gate dielectric, a first gate electrode layer, a barrier layer and a tensile metal or a silicide.