Characterization of n+-GaN/p−-SiC and n+-GaN/p+-SiC heterojunctions as well as fabrication of GaN/SiC heterojunction bipolar transistors (HBTs) using these heterojunctions is presented. The electroluminescence spectrum from n+-GaN/p+-SiC heterojunction diodes under forward bias clearly indicates electron injection from n+-GaN into p+-SiC. HBTs consisting of n+-GaN emitter /p+-SiC base/n−-SiC collector/n+-SiC substrate have been fabricated. Although clear common-base properties were obtained, the current gain was very low (10-4). SiC homojunction bipolar junction transistors (BJT) using the same base-collector junction exhibited a current gain value of 0.5, suggesting the low current gain of GaN/SiC HBTs originates from low emitter efficiency.