Scaling of CMOS device channel lengths can result in increased threshold voltage shifts after exposure to total dose radiation. An analytical model has been developed in order to predict these threshold voltage changes as a function of gate length and total dose for both gate oxide and parasitic thick field oxide transistors. Measurements show large increases in threshold voltage shifts after irradiation as gate lengths are decreased. The model is proven accurate to a total dose level of 106 rads (SiO2) and gate lengths down to 0.9 um. Scaling of field oxide gate lengths can have a severe impact on total dose hardness.