When a thin oxide is subjected to heavy ion irradiation, a large leakage current similar to the soft breakdown can be produced. In this work, we have studied the radiation soft breakdown (RSB) after 257 MeV Ag and I irradiation by using a quantum point contact (QPC) model, which also applies to hard and soft breakdown produced by electrical stresses. We have also studied the temperature dependence of RSB current from 98 K up to room temperature, and found that the gate current after irradiation is strongly reduced by decreasing temperature. It is shown that this behavior can be attributed to a temperature dependence of the carriers supplied from the cathode rather than to a temperature-induced modification of the size and/or shape of the oxide RSB paths. © 2001 American Institute of Physics.