The operation of transistorized Marx-bank circuits (MBCs) is analyzed, and physics-based modeling is used to understand the anomalous switching behavior of the first stage single trigger avalanche transistors of MBCs at high-current-injection conditions. The role of a voltage trigger pulse having variable rise time when applied to the base terminal is investigated to model the underlying physics of the anomalous switching behavior. Experimental observations related to ultrafast anomalous switching mechanisms of trigger transistor, i.e., either primary breakdown or current mode secondary breakdown, for faster and slower base drives are presented. This demonstrates the importance of the dynamic avalanche process and reverse saturation current on the switching mechanism under high-speed base-trigger ramps for different avalanche BJTs from various manufacturers and different lots. The agreement between 2-D TCAD device simulation results and the experimental observations shows the validity of the proposed theory when the base width and mobile carrier recombination rate are used as parameters in the device simulation setup. © 1973-2012 IEEE.