SnO2 has attracted considerable attention due to its wide bandgap, large exciton binding energy, and outstanding electrical and optoelectronic features. Owing to the lack of reliable and reproducible p-type SnO2, many challenges on developing SnO2-based optoelectronic devices and their practical applications still remain. Herein, single-crystal SnO2 microwires (MWs) are acquired via the self-catalyzed approach. As a strategic alternative, n-SnO2 MW/p-GaN heterojunction was constructed, which exhibited selectable dual-functionalities of light-emitting and photodetection when operated by applying an appropriate voltage. The device illustrated a distinct near-ultraviolet light-emission peaking at ∼395.0nm and a linewidth ∼50nm. Significantly, the device characteristics, in terms of the main peak positions and linewidth, are nearly invariant as functions of various injection current, suggesting that quantum-confined Stark effect is essentially absent. Meanwhile, the identical n-SnO2 MW/p-GaN heterojunction can also achieve photovoltaic-type light detection. The device can steadily feature ultraviolet photodetecting ability, including the ultraviolet/visible rejection ratio (R360nm/R400nm) ∼1.5×103, high photodark current ratio of 105, fast response speed of 9.2/51 ms, maximum responsivity of 1.5 A/W, and detectivity of 1.3×1013 Jones under 360 nm light at -3V bias. Therefore, the bifunctional device not only displays distinct near-ultraviolet light emission, but also has the ability of high-sensitive ultraviolet photodetection. The novel design of n-SnO2 MW/p-GaN heterojunction bifunctional systems is expected to open doors to practical application of SnO2 microstructures/nanostructures for large-scale device miniaturization, integration and multifunction in next-generation high-performance photoelectronic devices.