The metal-oxide-semiconductor field-effect transistor (MOSFET) and the parasitic bipolar transistor of domestic complementary metal oxide semiconductor (CMOS) process are irradiated with 60Coγ rays to investigate the failure mechanism of the mixed-signal ICs fabricated by deep submicron CMOS process, caused by total dose radiation. The research results are as follows. 1) The parasitic sidewall and top corner regions contribute to the intra-device leakage. 2) The parasitic bipolar transistor of CMOS process is not sensitive to total dose radiation, which is very different from the conventional bipolar transistor. Preliminary analysis suggests that the difference originates from the differences in the structural and making process. 3) The total dose radiation damage to the parasitic bipolar transistors is not coupled with the damage to the NMOS transistor in the same CMOS process. 4) Based on the above study, the radiation failure mechanisms of the analog and digital module in mixed-signal ICs fabricated respectively by the domestic and commercial CMOS process are investigated. Preliminary analysis suggests that the increase of off-leakage current of MOSFET is responsible mainly for the increase in power consumption of digital module, and the insensitivity of bandgap voltage reference to total dose radiation originates from the radiation resistance of the parasitic bipolar transistor which is the important part of bandgap voltage reference in CMOS mixed-signal ICs.