Unintentionally doped AlGaN thin films are grown on c-plane (0001) sapphire substrate by metal-organic chemical vapor deposition, and low-temperature AlN is deposited onto sapphire substrate used as a buffer layer. AlGaN metal-semiconductor-metal ultraviolet photodetectors with Ni/Au interdigitated contact electrodes are then fabricated by lift-off technology. The dark current of the AlGaN photodetectors is 5.61 \times 10-9 A at 2-V applied bias and the peak response occurrs at 294 nm.