A method includes providing a fin, an isolation structure, and first and second source/drain (S/D) features over the fin; forming an etch mask covering a first portion and exposing a second portion of the fin; removing the second portion of the fin, resulting in a first trench; filling the first trench with a first dielectric feature; removing the etch mask; and applying etching process(es) to remove the first portion of the fin and to partially recess the first S/D feature. The etching process(es) includes an isotropic etching tuned selective to materials of the first S/D feature and not materials of the isolation structure and the first dielectric feature, resulting in a second trench under the first S/D feature and having a gap between a bottom surface of the first S/D feature and a top surface of the isolation structure. The method further includes forming a via in the second trench.