The present disclosure describes a semiconductor device that includes a semiconductor device that includes a first transistor having a first gate structure. The first gate structure includes a first gate dielectric layer doped with a first dopant at a first dopant concentration and a first work function layer on the first gate dielectric layer. The first gate structure also includes a first gate electrode on the first work function layer. The semiconductor device also includes a second transistor having a second gate structure, where the second gate structure includes a second gate dielectric layer doped with a second dopant at a second dopant concentration lower than the first dopant concentration. The second gate structure also includes a second work function layer on the second gate dielectric layer and a second gate electrode on the second work function layer.