An enhanced threshold shift was observed in irradiated (total-ionizing-dose) 130 nm partially depleted silicon-on-insulator I/O nMOSFETs after 3000 s channel hot-carrier stress. This phenomenon was caused by the irradiation-induced additional channel lucky electrons which were injected in the silicon dioxide layers (STI/BOX/gate oxide). Mechanism of formation of greater substrate current in irradiated narrow devices was discussed. Accordingly, a model (enhanced lucky-electron model/Hot carrier injection effect) applied to devices in radiation space environment is established.In addition, the unusual phenomenon in irradiated devices with wide channel was also discussed. © 2020 The Japan Society of Applied Physics V ds = 4.45 V, gate voltage with maximum substrate current was thus determined as 1.1 V and 1.6 V for wide and narrow devices, respectively. Electrical stress was periodically interrupted to measure I-V characteristics of the devices.