1. A semiconductor structure comprising: a semiconductor substrate comprising a semiconductor material; a gate dielectric comprising a high dielectric constant (high-k) dielectric layer having a dielectric constant greater than 7.5 and located on said semiconductor substrate; and a gate electrode abutting said gate dielectric and including a lower metal layer abutting said gate dielectric, a scavenging metal layer abutting said lower metal layer, and an upper metal layer abutting said scavenging metal layer, wherein said scavenging metal layer includes a metal (M) for which the Gibbs free energy change of the reaction, Si+2/y M x O y →2x/y M+SiO 2 , is positive, and wherein Gibbs free energy per oxygen atom for formation of an oxide for said metal is equal to or more negative than Gibbs free energy per oxygen atom for formation of an oxide of a first elemental metal within a first metallic compound in said lower metal layer and is equal to or more negative than Gibbs free energy per oxygen atom for formation of an oxide of a second elemental metal within a second metallic compound in said upper metal layer.