Semiconductor devices and methods are provided. A semiconductor device according to the present disclosure includes a first transistor having a first gate dielectric layer, a second transistor having a second gate dielectric layer, and a third transistor having a third gate dielectric layer. The first gate dielectric layer includes a first concentration of a dipole layer material, the second gate dielectric layer includes a second concentration of the dipole layer material, and the third gate dielectric layer includes a third concentration of the dipole layer material. The dipole layer material includes lanthanum oxide, aluminum oxide, or yttrium oxide. The first concentration is greater than the second concentration and the second concentration is greater than the third concentration.