Using 3-D mixed-mode simulation, bipolar amplification effect in an inverter chain of single event transient(SET) is studied, and compared with that in single NMOS. It is found that bipolar amplification component takes a large proportion in SET current pulse, but not in an inverter chain. The difference of source/substrate biases between them and the mechanism of amplification are explained, which validates the conclusion that bipolar amplification depends on the bias of source/substrate. The positive current component from source to drain and the mechanism of SET pulse are also studied, and results show that the source current change is positive in the plateau region because of the presence of carrier diffusion.