A diamond-based field effect transistor, comprising a high-resistance diamond substrate, a conductive layer, a gate dielectric layer, a source electrode, a drain electrode and a gate electrode, an upper surface of the high-resistance diamond substrate being covered with the conductive layer, an upper surface of the conductive layer being provided with the source electrode, the drain electrode and the gate electrode, the gate dielectric layer being disposed between the gate electrode and the conductive layer, wherein a photocatalyst dielectric layer is provided on a region of the conductive layer between the source electrode and the gate electrode and on a region of the conductive layer between the drain electrode and the gate electrode.