Generally, the subject matter disclosed herein relates to modern sophisticated semiconductor devices and methods for forming the same, wherein a reduced threshold voltage (Vt) may be achieved in HK/MG transistor elements that are manufactured based on replacement gate electrode integrations. One illustrative method disclosed herein includes forming a first metal gate electrode material layer above a gate dielectric material layer having a dielectric constant of approximately 10 or greater. The method further includes exposing the first metal gate electrode material layer to an oxygen diffusion process, forming a second metal gate electrode material layer above the first metal gate electrode material layer, and adjusting an oxygen concentration gradient and a nitrogen concentration gradient in at least the first metal gate electrode material layer and the gate dielectric material layer.