AlGaN/GaN heterostructure field-effect transistor has great potential for use in high voltage, high current and high power device applications. To reduce the gate leakage current, generally oxide layers are employed. Using an Al(2)O(3) layer as a gate oxide layer, effects on the device performances were investigated. Leakage current density and current-voltage characteristics of AlGaN/GaN heterostructure field-effect transistor with Al(2)O(3) layer were measured, the drain current was about 5 10 mA/mm at V(gs)= 1 V and the gate leakage current density was lowered with Al(2)O(3) layer. (c) 2008 Elsevier B.V. All rights reserved.