A model for the on-state behavior of super-junction structures, based on the theory of the long-channel MET, is derived and compared with the results of TCAD simulations. The limits to the on-state operation of Si and SiC super-junction devices are explored using the model to determine the maximum current density compatible with an assumed level of device power dissipation. Comparisons are made with conventional FET devices based on the product of the maximum on-state current and breakdown voltage (switched power capability). Results show that super-junction devices can demonstrate significantly increased switched power capability over a wide range of breakdown voltage provided the doping imbalance error can be limited to less than 1%.