The impact of collector-emitter voltage VCE, bias conditions on total ionizing dose TID, in bipolar junction transistors BJTs, was investigated. The BJTs are set at forward active mode of base-emitter voltage VBE, swept from 0 to 1.0 V at different biased conditions of VCE, ranging from 1V to 2 V at an interval of 0.25V during 60Co γ irradiation tests. The damage mechanism of TID in BJTs at different VCE bias conditions were analyzed by forward Gummel characteristics, forward current gain βf, normalized excess base current ΔIB/IBpre, normalized current gain βfpost/βfpre and ideality factor n. The results show that the increments of base current ΔIB, and collector current ΔIC, are slightly different in various TID VCE bias conditions which also effects slight changes in their current gain Δβf, degradation. However, the degradation effect was noticed more in low bias VBE than high VBE with no significant difference. This is attributed to different degradation produced and accumulated in oxide spacer of BJT. The ΔIB/IBpre and βfpost/βfpre show similar trend of different VCE bias conditions resulting into varying distribution of interface traps Nit, at Si-SiO2 interface of the BJT under TID influence. The ideality factor n, for excess base current ΔIB, is ~2 for VBE from 0.35V to 0.6V at different VCE bias conditions. Thus, ideality factor n, slightly increases as the VCE bias rises and decreases with rising TID after Nit reaches saturation of 130krad (Si) in BJT. The 130krad (Si) low total dose’s ideality factor is closer to 2 than other increasing TID values.