The basic design criteria for high-power gate turn-off (GTO) thyristors are discussed. Results of a Study of the influence of thep-base on gate avalanche voltage show that only a narrow range of voltages are possible. The importance of the cell array in determining debiasing effects on the gate electrode, and its effects on gate current density, are illustrated. Finally, the switching performance of 2500 V and 4500 V GTO thyristors with varying anode shorting efficiencies is examined.