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High-voltage (4-6 kV) 4H-SiC-based bipolar junction transistors were designed, fabricated, and characterized. Various design and process optimization techniques to improve the on state and the forward blocking performance of these devices were studied and incorporated. Using the conventional base contact implantation process, devices with blocking voltages up to 4 kV and specific on-resistance (R on, sp) values higher than the unipolar limit (37 mOmegamiddotcm2), with a current gain of ten in the active region, were experimentally demonstrated. A novel selective growth of p-contact-based process was developed and implemented. This, coupled with improvements in the termination design, resulted in enhancing the blocking voltage capability to 6 kV while simultaneously lowering the R on, sp to below the unipolar limit (28 mOmegamiddotcm2 and current gain of four in the active region), for the same starting material. Evidence for the presence of conductivity modulation (for the first time) in high-voltage SiC BJTs was also shown experimentally.