The present disclosure provides semiconductor device and methods of forming the same. A semiconductor device according to the present disclosure includes a gate structure, a source/drain feature adjacent the gate structure, a dielectric layer disclosed over the gate structure and the source/drain feature, a gate contact disposed in the dielectric layer and over the gate structure, and a source/drain contact disposed in the dielectric layer and over the source/drain feature. The dielectric layer is doped with a dopant and the dopant includes germanium or tin.