In this work, tin oxide (SnO₂) nanoarrays (NAs) with a novel morphology were fabricated by a hydrothermal method. Each SnO₂ nanorod (NR) consisted of a bunch of nearly ten primary NRs with a width of 4–7 nm. On this basis, gold (Au) nanoparticles (NPs) were used to induce the growth of smaller and more orderly SnO₂ NAs. The prepared ultraviolet (UV) detectors based on SnO₂ NAs have high responsivity and high external quantum efficiency (EQE) under 20 μW cm⁻² UV light with only 1 V external bias voltage.