Metal-semiconductor diode of Au/n-GaAs is studied under the irradiation of swift heavy ion (SHI) beam (80 MeV O-16(6+)), using in situ current-voltage characterization technique. The diode parameters like ideality factor, barrier height, and leakage current are observed to vary with irradiation fluence. Significantly, the diode performance improves at a high fluence of 2 x 10(13) ions cm(-2) with a large decrease of reverse leakage current in comparison to the original as deposited sample. The Schottky barrier height (SBH) also increases with fluence. At a high irradiation fluence of 5 x 10(13) ions cm(-2) the SBH (0.62 +/- 0.01 eV) is much larger than that of the as deposited sample (0.55 +/- 0.01 eV). The diode parameters remain stable over a large range of irradiation up to fluence of 8 x 10(13) ions cm(-2). A prominent annealing effect of the swift ion beam owing to moderate electronic excitation and high ratio of electronic energy loss to the nuclear loss is found to be responsible for the improvement in diode characteristics. (c) 2007 Elsevier B.V. All rights reserved.