The effect of radiation-introduced defects on the behaviour of HfO2-based metal-insulator-metal (MIM) capacitors as a function of gamma-ray radiation dose from 10 to 1000 krad are reported. Half the capacitors studied showed no degradation after exposure to 1000 krad from a 60Co source, whilst the remaining half showed no change to parameters, such as barrier height and dielectric constant. For the good devices, the I-V characteristics are controlled by Poole-Frenkel model, at a corresponding interface trap energy of 0.39 ~ 0.46 eV before radiation and 0.37 ~ 0.44 eV after 1000 krad. The failed devices show an substantial increase in the trap density from the as fabricated level of 1019 cm-3 to in excess of 1020 cm-3, in contrast to the good devices which show almost no change. We relate this change in defect density to the failure of devices by means of a percolation model, with a trap separation of around 2 nm.