The mymargin metal–oxide–semiconductor mymargin (MOS)-controlled thyristor (MCT) has been characterized by MOS gating, high current rise rate, and high blocking capabilities. The anode-short MCT (AS-MCT) is distinguished from the conventional MCT by an anode-short structure, which forms an extracting path for the electron current at the gate ground and develops a normally-OFF characteristic. As a composite structure made of MOS and bipolar junction transistors, the AS-MCT is susceptible to ionization damage. The total ionization dose (TID) effects on the XND1 AS-MCT (breakdown voltage 1800 V grade) with a dose up to 9160 Gy(SiO ₂ ) are reported. The experimental results of transfer, forward conductive, and forward blocking characteristics are presented. A novel phenomenon, denoted as “self-trigger”, is identified for the AS-MCT following -ray exposures, which can account for the significant increase in anode current in the AS-MCT. This article proposes the mechanism behind the characteristic degradation from the TID damage in the AS-MCT, from a device physics perspective.