The reset switching probability of resistive switching devices is characterized in array testing. The measured switching probability can be quantitatively explained based on the mechanism of a thermally activated reset process. An analytical model of switching probability is developed to describe the dependence of reset probability on operation parameters, including applied voltage, selection transistor gate voltage, and pulsewidth. The close fitting of the model with measurement also confirms the thermal reset mechanism. This quantitative switching probability model can be used to extrapolate key device parameters and may provide important guidance in yield improvement and memory evaluation.