The aim of this study is to determine the reverse-bias leakage current conduction mechanisms in Au/SiO2/n-GaAs metal-insulator-semiconductor type Schottky contacts. Reverse-bias current-voltage measurements (I-V) were performed at room temperature. The using of leakage current values in SiO2 at electric fields of 1.46-3.53 MV/cm, ln(J/E) vs. √E graph showed good linearity. Rom this plot, dielectric constant of SiO2 was calculated as 3.7 and this value is perfect agreement with 3.9 which is value of SiO2 dielectric constant. This indicates, Poole-Frenkel type emission mechanism is dominant in this field region. On the other hand, electric fields between 0.06-0.73 and 0.79-1.45 MV/cm, dominant leakage current mechanisms were found as ohmic type conduction and space charge limited conduction, respectively. © 2013 Pleiades Publishing, Ltd.