The effects of ionizing radiation (gamma) on the operation of two‐phase stepped‐oxide surface‐channel charge‐coupled devices (CCD's) were studied. For total doses up to 105 rad (Si), the primary cause of changes in CCD operation is a negative shift in the flat‐band voltage, with the flat‐band voltage shift for the polysilicon electrodes being greater than that for the aluminum electrodes. For fixed applied voltages, the flat‐band voltage shifts cause (i) an increase in transfer inefficiency due to the cutoff of fat zero, and (ii) a decrease in the full‐well capacity due to the modified surface potential profile. Up to 105 rad, the preirradiation transfer inefficiency could be recovered by changing the input‐gate voltage to compensate for the flat‐band voltage shift. Up to 105 rad, no significant effects due to radiation‐induced interface states were observed; however, at 3 × 105 rad, increases in transfer inefficiency and dark current attributed to radiation‐induced interface states were observed.