The forward current-voltage (I-V) characteristics of Au/n-GaAs Schottky barrier diodes (SBDs) have been studied over a wide temperature range ( 80 - 300 K). The barrier height inhomogeneities by assuming a Gaussian distribution of barrier heights at the interface were observed. The evaluation of the experimental I-V data reveals a non-linear increase of the zero-bias barrier height (q Phi(0)). To remove the spatial inhomogeneity of the barrier height based on small regions or patches and to increase the barrier height compared to the reference sample Au/n-GaAs, the front surface of the n-type GaAs semiconductor has been oxidized by the anodic oxidation method and metal/insulating/semiconductor (MIS) Au/n-GaAs SBDs have been formed. The ln(I-0/T-2) versus 1/T and q Phi(0) versus T plots of the MIS have exhibited the linear behavior in the temperature range of 80 - 300 K. Thus, the I-V data of the MIS diodes have obeyed the interfacial layer model due to the interfacial layer and it has been concluded that the inhomogeneity of the barrier height can be disappeared by a formed interfacial layer at the metal and semiconductor interface.