When a ceramic oxide with an applied electric field is subjected to extended irradiation with energetic particles at elevated temperatures, the electrical conductivity has been reported to increase, a phenomenon termed radiation-induced electrical degradation ͑RIED͒. In the present study ␣-Al 2 O 3 crystals were subjected to 1800 V/cm while irradiated with 1.8 MeV electrons at 773 K. Above a critical dose the conductivity increased. During the conductivity enhancement, the applied field was reversed, resulting in a decrease in the conductivity. This result demonstrates that RIED was caused by carriers injected from the electrodes, in concert with electrons and holes created during ionizing irradiation. A model for RIED is proposed: the injected carriers are trapped mainly at impurities near the electrodes, leading to formation of dislocations. These dislocations serve as traps for electrons and holes generated during ionizing radiation. A network of interconnecting dislocations is associated with the enhanced conductivity.