Semiconductor device structures having metal gate structures with tunable work function values are provided. In one example, a semiconductor device includes a first gate structure and a second gate structure on a substrate; wherein the first gate structure includes a first gate dielectric layer having a first material, and the second gate structure includes a second gate dielectric layer having a second material, the first material being different from the second material, wherein the first and the second gate structures further comprises a first and a second self-protective layers disposed on the first and the second gate dielectric layers respectively, wherein the first self-protective layer comprises metal phosphate and the second self-protective layer comprises boron comprising complex agents and a first work function tuning layer on the first self-protective layer in the first gate structure.