A semiconductor structure includes a first transistor having a first source/drain (S/D) feature and a first gate; a second transistor having a second S/D feature and a second gate; a multi-layer interconnection disposed over the first and the second transistors; a signal interconnection under the first and the second transistors; and a power rail under the signal interconnection and electrically isolated from the signal interconnection, wherein the signal interconnection electrically connects one of the first S/D feature and the first gate to one of the second S/D feature and the second gate.