HfO2 thin film is deposited on p-Si substrates by RF magnetron sputtering apparatus and annealed at 750 °C for 10 min with O2 atmosphere. Spectral analysis shows that HfO2 thin films have good transmittance to light, especially ultraviolet band. The HfO2 layers belong monoclinic phase and its thickness is about 50 nm. In the Au/HfO2/p-Si structure, photodiode characteristics were studied at room temperature and compared with the light current generated under white light, the response current generated under ultraviolet light is more prominent. The photocurrent reaches 80 μA and the repeatable response of device under 23.5 mW/cm2 ultraviolet illuminating is stable. It's found that the working mechanism of this photodiode could have three different states: the majority carrier stacking state of reverse bias, the majority carrier depletion state of forward bias with dark condition and the minority carrier inversion state of forward bias with ultraviolet illumination. The device also has a high damage threshold and its photocurrent is still not saturated at bias 8 V, indicating that it can be applied as a new type of UV detector. Display omitted •A photodiode with an Au/HfO2/p-Si structure is fabricated.•The photocurrent increases with the intensity of ultraviolet light, with a maximum of 80 μA.•This photodiode also has a high damage threshold and its photocurrent is still unsaturated at an 8 V bias.