A semiconductor transistor device including a channel structure, gate structure, a first source/drain structure, a second source/drain structure, and a back-side source/drain contact. The gate structure overlies the channel structure. The first source/drain structure and the second source/drain structure are disposed on opposite endings of the channel structure. The back-side source/drain contact is disposed under the first source/drain structure. A line lies across the gate structure and the first source/drain structure. The line is parallel to an upper surface of the gate structure.