The scaling of transistors with thinner channel thicknesses has led to a surge in research on two-dimensional (2D) and quasi-2D semiconductors. However, modulating the threshold voltage (V T) in ultrathin transistors is challenging, as traditional doping methods are not readily applicable. In this work, we introduce a optical-thermal method, combining ultraviolet (UV) illumination and oxygen annealing, to achieve broad-range V T tunability in ultrathin In2O3. This method can achieve both positive and negative V T tuning and is reversible. The modulation of sheet carrier density, which corresponds to V T shift, is comparable to that obtained using other doping and capacitive charging techniques in other ultrathin transistors, including 2D semiconductors. With the controllability of V T, we successfully demonstrate the realization of depletion-load inverter and multi-state logic devices, as well as wafer-scale V T modulation via an automated laser system, showcasing its potential for low-power circuit design and non-von Neumann computing applications.