The principle of operation of the transistor-based Marx bank circuit has been examined. It was experimentally observed that stage-wise increase of reverse voltage does not occur. This cannot be explained by the principle of operation understood so far. A new explanation, consistent with the experimental observations and associating current-mode second breakdown of transistors, is proposed. A few experimental observations made by earlier workers have also been justified in light of the new current-controlled mechanism. © 1998 American Institute of Physics.