Electric characteristics of devices in advanced CMOS technologies change over the time because of the impact of the ionizing radiation effects. Device aging is caused by cumulative contribution of generation of defects in the gate oxide and/or at the interface silicon-oxide. The concentration of these defects is time and bias-dependent values. Existing models include these effects through constant shift of voltage threshold. A method for including ionizing radiation effects in Spice models of MOS transistor and FinFET, based on an auxiliary diode circuit using for derivation of values of surface potential, that also calculates the correction time-dependent voltage due to concentration of trapped charges, is shown in this paper.