This paper describes group-III nitride (III-N)/SiC heterointerface and its device applications. Heteroepitaxial growth of III-N on SiC opens new opportunity of SiC-based heterojunction devices such as heterojunction bipolar transistors (HBTs). The authors developed growth methods to grow high-quality III-N on SiC by molecular-beam epitaxy. Fabricated GaN/SiC heterojunction exhibited type-II band-lineup. By using AlN/GaN short period superlattice as a quasi AlGaN alloy, the authors successfully controlled the band-lineup to be type-I and demonstrated common-emitter-mode operation of III-N/SiC HBTs.