Semiconductor micro/nanowire is an attractive candidate for light-emitting devices (LED), especially laser diodes, due to its ideal geometric shape, excellent optical performance, and electrical transport properties. However, the realization of single micro/nanostructure semiconductor LED or lasers is still a challenge topic. In this Letter, we demonstrated a feasible route to fabricate electrically injection single microwire (MW) light-emitting devices. First, the excellent optical properties of single MW were investigated comprehensively, especially for the self-formed high-Q whisper gallery mode lasing. By properly engineering the band alignment of MW/p-GaN heterojunction using a dielectric MgO interlayer, the effective carrier injection and excitonic-type recombination electroluminescence was realized in the single MW active media. Our results present a significant step toward future fabrication of single micro/nanowire LED and laser diode.