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.