High-performance solar-blind (200–280 nm) avalanche photodetectors (APDs) were fabricated based on highly crystallized ZnO–Ga2O3 core–shell microwires. The responsivity can reach up to 1.3 × 103 A/W under −6 V bias. Moreover, the corresponding detectivity was as high as 9.91 × 1014 cm·Hz1/2/W. The device also showed a fast response, with a rise time shorter than 20 μs and a decay time of 42 μs. The quality of the detectors in solar-blind waveband is comparable to or even higher than that of commercial Si APD (APD120A2 from Thorlabs Inc.), with a responsivity ∼8 A/W, detectivity ∼1012 cm·Hz1/2/W, and response time ∼20 ns. The high performance of this APD make it highly suitable for practical applications as solar-blind photodetectors, and this core–shell microstructure heterojunction design method would provide a new approach for realizing an APD device.