In this paper, we extensively characterize and model the threshold voltage instability in lateral β-Ga₂O₃ MOSFETs with Al₂O₃ gate dielectric. Specifically, (i) the results indicate that the threshold voltage instability originates from electron trapping at gate dielectric border traps close to the Al₂O₃/β-Ga₂O₃ interface. (ii) Logarithmic kinetics were detected for both stress and recovery by means of a innovative fast-capacitance experimental setup, over more than seven decades of time; (iii) a generalized model, which is capable of accurately reproducing the experimental results, was proposed to explain this trend.