Transparent solar-blind ultraviolet photodetectors (SBUV PDs) have extensive applications in versatile scenarios, such as optical communication. However, it is still challenging to simultaneously achieve high responsivity, high transparency, and satisfying self-powered capability. Here, we demonstrated high-performance, transparent, and self-powered photoelectrochemical-type (PEC) SBUV PDs based on vertically grown ultrathin In₂O₃ nanosheet arrays (NAs) with a three-dimensional (3D) porous structure. The 3D porous structure simultaneously improves the transmittance in the visible light region, accelerates interfacial reaction kinetics, and promotes photogenerated carrier transport. The performance of In₂O₃ NAs photoanodes exceeds most reported self-powered PEC SBUV PDs, exhibiting a high transmittance of approximately 80% in the visible light region, a high responsivity of 86.15 mA/W for 254 nm light irradiation, a fast response speed of 15/18 ms, and good multicycle stability. The In₂O₃ NAs also show excellent spectral selectivity with an ultrahigh solar-blind rejection ratio of 1319.30, attributed to the quantum confinement effect induced by the ultrathin feature (2–3 nm). Furthermore, In₂O₃ NAs photoanodes show good capability in underwater optical communication. Our work demonstrated that a 3D porous structure is a powerful strategy to synchronously achieve high responsivity and transparency and provides a new perspective for designing high-performance, transparent, and self-powered PEC SBUV PDs.