The detection and quantification of UVA radiation are indispensable for the reason that excess UVA radiation is harmful to skin, eyes, immune system and blood vessels of the human body. This study demonstrates a high-performance and accurate UVA (320–400 nm) detector based on polycrystalline CH₃NH₃PbCl₃/α-Ga₂O₃ nanorod array hybrid structure, which was fabricated by using facile and low-cost solution processing method. The devices show the maximum responsivity of 8.02 mA/W under zero bias, which is two orders of magnitude larger than bare polycrystalline CH₃NH₃PbCl₃ photodetector, as well as high speed photo-switching. Meanwhile, the detectivity of this self-powered device reaches up to 1.9 × 10¹¹ Jones, which is even superior to most of the reported single-crystal CH₃NH₃PbCl₃ photodetectors. This study reveals the potential in the combination of ultra-wide bandgap inorganic semiconductors with polycrystalline organic–inorganic hybrid perovskites in high performance of photodetector and other optoelectronic devices.