VVMOS transistor is a new type of high frequency power MOS transistor with vertical channels at the surface of the V-groove. Like other MOSFET s, one of the important features is no secondary breakdown, However, these is negative resistance breakdown, effect in MOSFET's is reported recently by some authors. The reported effects may eause secondary breakdown, and result in destructive damage to the de-vices.While measuring the VVMOSFET s made in our laboratory, we have also observed the destructive negative resistance breakdown effect. And model based on the effect of parasitic vertical bipolar npn transistor is proposed to explain this effect. Some using these method, the negative resistance breakdown effect has been lowered of even eliminated, and thus the proposed negative resistance breakdown model for VVMOSFET's is verified.