Abstract The electrical characteristics of bulk nFinFETs after total-ionizing-dose (TID) irradiation were experimentally evaluated with respect to the process variation (PV). The inconsistent transfer characteristics, particularly the different threshold voltage shifts under an identical bias condition and irradiation dose, were investigated through technology computer aided design (TCAD) simulation, considering the shallow trench isolation (STI) footing and the asymmetrical sidewall. The influence that the bias condition had, as an important factor including ON, OFF, and transmission gate (TG), is included in this paper to better illustrate the PV dependence. The HfO 2 high-ĸ metal gate, the STI, and the PV dependent geometry were some of the influences that occurred within the degradation of electrical performances as the TID increased. A radiation-hardness strategy was proposed in order to improve the electrical properties of the FinFET devices in the radiation environments.