The aim of the presented research was to develop a faithful SPICE simulation model of radiation and post-irradiation effects in a low-dropout voltage regulator with a vertical serial PNP transistor. The main parameters for the analysis of the circuit’s radiation response were the voltage regulator’s maximum output current and the minimum dropout voltage, as well as the serial transistor’s excess base current. All the data, comprised of the old irradiation and new annealing results, were unified and normalised, in order to enable a broad insight in the radiation tolerance of the examined circuits. Initial radiation effects, as well as the late post-irradiation effects, were successfully simulated using the variations of the maximum forward emitter current gain and knee current of the serial PNP power transistor. Ten-year room temperature annealing led to a significant recovery of the serial transistor’s excess base current, yet the maximum output current and minimum dropout voltage, in most cases, expressed further degradation. On the other hand, two short-term, high-temperature annealing periods led to the tremendous recovery of all of the irradiated voltage regulators, reducing the circuit degradation down to the level perceived after absorption of nearly 10% of the total ionising dose.