A GaN-based Schottky barrier diode (SBD) with a 5-pair AlGaN–GaN intermediate layer for ultraviolet (UV) photodetector (PD) was fabricated and investigated. It was found that we could achieve a smaller dark leakage current and noise level by using the 5-pair AlGaN–GaN intermediate layer. For our device biased at −5 V, the responsivity at 360 nm was found to be 0.26 A/W and the UV-to-visible rejection ratio was estimated to be 1.83 × 104. At the same bias, it was found that minimum noise equivalent power and normalized detectivity of our device were 1.00 × 10−9 W and 1.45 × 109 cm Hz0.5 W−1, respectively. This indicates a simple and effective way to fabricate high-performance PDs for UV detection.