A theory of the switching respinse of the CBMOST (OR COOLMOST, or Super Junction device) is proposed based on the physical nd geo-metracal parameters inherent in the voltage sustaining structure. It is proven that the salient feature of such a device is that the storage time in turn-off process is a little longe than the conventional power Most due to its heavier doping. Explanation for the fast turn-on Process DESPITE OF Having an oppositely doped region inside the voltage sustaining layer is also given. It is also shown that if p-(or n-) regions in the CB-sturcture are not directly contacted to the n+(or p+) drain region. Then device is a normally-on one. Measures are proposed for the real device to be not normally-on.