A technique for achieving tunable threshold voltage (VTH) is investigated in a gate-all-around device, which is a representative floating body structure. For this concept, the in-plane gate is designed to be both a driving gate and a control gate. The control gate governs the potential distribution along the gate electrode, which acts as a built-in voltage divider in the MOSFET. During the VTH tuning by the control gate, there is no electrical performance degradation, and modulation of VTH follows a nearly perfect linear tendency. The results are verified by the electrical measurements of the fabricated device and a multi-physics simulator.