A rad-sensitive sub-threshold model for the partially depleted, SOI n-channel MOSFET, based on existing pre irradiated device models is presented for applications in low power CMOS circuit designs. The model is continuous from sub-threshold to strong inversion regions and includes the radiation-induced oxide trapped charge, interface state charge, floating body effects and associated parasitic such as BJT. To demonstrate the applicability of the model, we have made an attempt to explain the sub-threshold current-voltage characteristics of a typical SOI n-MOSFET under a total dose condition. The calculated shift of sub-threshold characteristics to more negative values with dose with respect to pre-irradiated condition agrees with the experimentally observed behavior reported in the literature. (C) 2000 Elsevier Science Ltd. All rights reserved.