Abstract: When trying to explain the latch-up window phenomena in CMOS devices induced by radiation, the so called “three-path” latch-up window model is provided. The “three-path” latch-up window model is simply based on the analysis of CMOS device latch-up circuit model. To verify the model, a test circuit has been designed to simulate parasitical latch-up paths in CMOS devices and relevant parameters are reported. Transient gamma irradiation experiment on “Qiangguang I” indicates that a latch-up window appears in the test circuit as predicated. The result validates that it is reasonable to explain some latch-up window phenomena according to the “three-path” latch-up window model．