Schottky barrier structures formed on epitaxial GaAs:Sb have been studied at different Sb concentrations (0-1x10(20) cm(-3)) and different temperatures (80-300 K). Current-voltage (I-V) characteristics have been numerically simulated and compared with the experimental measurements in an attempt to reveal the dominant current transport mechanism. Since Sb is a nonelectrically active dopant in GaAs but efficiently influences defect ensemble, the role of the defects on the electrical characteristics of the device structures could be investigated. Three different regions of Sb doping have been considered in accordance with a previous study of the structural and electronic properties of metal organic vapor phase epitaxy-grown GaAs:Sb. The current transport in the samples containing an optimum amount of Sb (respectively, minimum defects) is dominated by a thermionic field emission in the main operation bias range, although indications of Poole-Frenkel effect are observed, related to the intrinsic near mid-gap electron levels. In the undoped and highly doped samples the current is mainly due to a carrier diffusion mechanism. In addition, the large amount of defects in these samples results in an electron tunneling component which is present in the I-V characteristics.