Abstract: Bulk complementary metal-oxide-semiconductor (CMOS) integrated circuits contain the parasitic silicon-controlled-rectifier (SCR) structure, which tend to latch-up, even burn out, when they are exposed to transient gamma irradiation. Therefore, it is significant to study latch-up prevention. The continuity equation based on the minority carrier in parasitic transistors was solved, the duration of photocurrent in the SCR structure was calculated, and the condition of auto-feed-back preventing the devices’ latch-up was confirmed. Moreover, the relationship of the condition and dose rate was concluded. Two kinds of circuits which were SCR’s equivalent circuit and CMOS circuit were irradiated by transient gamma rays. The experimental results match the theoretical results well.