This work reports a low-temperature route for semiconducting SnO₂ thin-film transistors (TFTs) using a solution-processed precursor with alkali hydroxide pre-treatment. A brief KOH step prior to annealing regulates the chemical and morphological evolution of SnCl₂-derived films. KOH treatment promotes ligand exchange, surface dehydration, and removal of residual chloride species, enabling reconstruction of a continuous Sn–O–Sn network during annealing. These transformations suppress oxygen-deficient donor states, yielding stable semiconducting behavior and improved gate modulation under low-temperature processing. The results demonstrate that controlled surface chemistry and morphology are critical for defect regulation in solution-derived SnO₂ TFTs.