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Polarization-sensitive photodetectors are the core of optics applications and have been successfully demonstrated in photodetectors based on the newly-emerging metal-halide perovskites. However, achieving high polarization sensitivity is still extremely challenging. In addition, most of the previously reported photodetectors were concentrated on 1D lead-halide perovskites and 2D asymmetric intrinsic structure materials, but suffered from being external bias driven, lead-toxicity, poor stability and complex processes, severely limiting their practical applications. Here, we demonstrate a high-performance polarization-sensitive and stable polarization-sensitive UV photodetector based on a dendritic crystal lead-free metal-halide CsCu 2 I 3 /GaN heterostructure. By combining the anisotropic morphology and asymmetric intrinsic structure of CsCu 2 I 3 dendrites with the isotropic material GaN film, a high specific surface area and built-in electric field are achieved, exhibiting an ultra-high polarization selectivity up to 28.7 and 102.8 under self-driving mode and -3 V bias, respectively. To our knowledge, such a high polarization selectivity has exceeded those of all of the reported perovskite-based devices, and is comparable to, or even superior to, those of the conventional 2D heterostructure materials. Interestingly, the unsealed device shows outstanding stability, and can be stored for over 2 months, and effectively maintained the performance even after repeated heating (373K)-cooling (300K) for different periods of time in ambient air, indicating a remarkable temperature tolerance and desired compatibility for applications under harsh conditions. Such excellent performance and simple method strongly show that the CsCu 2 I 3 /GaN heterojunction photodetector has great potential in practical applications with high polarization-sensitivity. This work provides a new insight into designing novel high-performance polarization-sensitive optoelectronic devices.