Siliconp+njunctions irradiated with fast‐neutron fluences (5×1011–5×1013neutrons/cm2) have been experimentally measured using the thermally stimulated current technique. When forward filling voltages are applied, a new peak is found in samples irradiated with fluences greater than 5.6×1011. A cluster model has been developed to describe the new peak and the cluster’s dimensions and defect concentrations have been evaluated.