Semiconductor device and the manufacturing method thereof are disclosed herein. An exemplary semiconductor device comprises a substrate having a first region and a second region; a first semiconductor fin formed on the substrate within the first region; a second semiconductor fin formed on the substrate within the second region; a first liner layer disposed along a lower portion of the first semiconductor fin and a lower portion of the second semiconductor fin; a second liner layer disposed over the first liner layer in the second region, wherein the second liner layer is different from the first liner layer in composition; and an isolation feature disposed on the first liner layer in the first region and on the second liner layer in the second region, and separating lower portions of the first semiconductor fin and the second semiconductor fin.