Two-inch semi-insulating SiC bulk crystals with resistivity higher than 1×106 Ωcm were achieved by vanadium doping during sublimation. Secondary-ion-mass-spectrometry (SIMS) was employed to determine the concen-tration of impurities in the crystals, such as B, Al, V and N. These results indicated that the concentration of nitrogen and aluminum kept on decreasing and the concentration of B and V was almost constant during the whole growth. An inner crucible was used to control the exhausting of vanadium, which made the uniformity of the high resistivity (>1×106 Ωcm) in the wafer up to 80%. High-performance AlGaN/GaN high-electron-mobility-transistor (HEMT) materials and devices were grown and fabricated on semi-insulating 6H-SiC sub-strates. The two-dimensional electron gas (2DEG) mobility at room-temperature was 1795 cm2/V·s. The charge carrier concentration of the substrate determined by capacitance-voltage (C-V) test was 7.3×1015 cm-3. The device with a gate width of 1 mm exhibits a maximum output power of 5.5 W at 8 GHz, which proves the semi-insulating property of the substrates indirectly. Secondary-ion-mass-spectrometry (SIMS) was used to determine the concen- tration of impurities in the crystals, such as as B, Al, V and N. These results indicated that the concentration of nitrogen and aluminum kept on decreasing and the concentration of B and V was almost constant during the whole growth. An inner crucible was used to control the exhausting of vanadium, which High-performance AlGaN / GaN high-electron-mobility-transistor (HEMT) materials and devices were grown and fabricated on semi-insulating 6H The two-dimensional electron gas (2DEG) mobility at room-temperature was 1795 cm2 / V · s. The charge carrier concentration of the substrate determined by capacitance-voltage (CV) test was 7.3 × 10 15 cm- 3. The device with a gate width of 1 mm exhib its a maximum output power of 5.5 W at 8 GHz, which proves the semi-insulating property of the substrates indirectly.