A study on Au/n-GaAs Schottky barrier diode (SBD) parameters with and without thin native oxide layer fabricated on n-type GaAs has been made. The native oxide layer with different thicknesses on chemically cleaned GaAs surface was obtained by exposing the GaAs surfaces to clean room air before metal evaporation, The native oxide thicknesses of samples AuD2, AuD3, AuD4, AuD5. and AuD6 are in the form AuD2<AuD3<AuD4<AuD5<AuD6 depending on the exposing time. The barrier height value has decreased with increasing the exposure time up to 10 days, and after 10 days, it remained about unchanged up to 45 days. Furthermore, depending on the ageing, the samples AuD5 (exposed to air for 30 days) and AuD6 (for 45 days) reached the equilibrium barrier value after 30 days metal deposition while samples AuD2 (for 5 days), AuD3 (for 10 days), and AuD4 (for 20 days) did not show any equilibrium value for the barrier height as a function of the ageing up to 105 days because dipole between the metal and semiconductor. that would modify the barrier height, disappears. This seems to be associated with the oxide layer thickness. Moreover, the carrier concentration value of the samples decreased with the increasing ageing time. (C) 2002 Elsevier Science B.V. All rights reserved.