The new quantitative model of influence of gate bias on the threshold shift of MOS-structures at the ionizing radiation which is based on the accounting of holes trapping in a thin border layer of gate dielectric on interface with a silicon substrate is developed. The model allows to describe the smooth growth of threshold shift with gate bias – approximately linear from a dose for a surface component and nonlinear for a volume component. The threshold shift at a negative gate bias is modelled on the basis of the accounting of holes generation at ionizing radiation in the border layer.