Scaling theory is applied in the design of power devices. The scaling law for power devices is presented. A new figure of merit (HFOM) is derived as an invariant of scale transformation, which is a function of avalanche breakdown field and regarded as a measure of the performance of a power device. The optimization of a SiC Schottky barrier diode with the floating junction structure (Super-SBD) has been performed using the HFOM as a measure of the performance. The performance of the optimized Super-SBD surpasses the performance limit of 4H-SiC devices with the conventional structure.