We have reported a study on current-voltage (I-V) characteristics and capacitance-voltage (C-V) of an Ni/n-GaAs Schottky barrier diode in a wide temperature (T) range of 100-320 K in steps of 20 K, which is prepared by a magnetron direct current sputtering technique. The ideality factor decreases and barrier height (BH) increases with an increase in the temperature. The variation of the diode parameters with the sample temperature has been attributed to the presence of the lateral inhomogeneities in the BH. It has been seen that the junction current is dominated by thermionic field emission. The carrier concentration, diffusion potential, BH, Fermi energy level and the temperature coefficient of the BH have been calculated from the temperature-dependent C-V-T characteristics.