The 4H-SiC bonded substrate (SiCkrest) manufactured by SICOXS comprises an extremely thin (less than 1-μm thickness) monocrystalline 4H-SiC layer bonded on an n-type low resistivity polycrystalline 3C-SiC substrate by the surface activated bonding method. Such a unique hybrid structure is expected to bring some benefits that are not possible with a conventional 4H-SiC bulk substrate, such as reduction of on-state resistance in PiN diodes and reduction of forward bias degradation in PiN diodes. In this study, we focus on contact resistance between polycrystal and backside metal Ni/Ti of 4H-SiC bonded substrates and its temperature dependence. The circular TLM method was used to measure the backside contact resistance in order to improve the accuracy of the measurement. As result, bonded substrates have the low resistance backside contact can be formed without annealing, and no change in backside contact resistance at high temperature. In addition, the effects of on-state resistance reduction on power devices were evaluated by SBDs of bonded substrates. Unannealed bonded-SiC can reduce VF by 13% compared with annealed mono-SiC. These results suggest that the 4H-SiC bonded substrate can be greatly advantageous in reducing of on-state resistance of SiC power devices.