Metal-semiconductor field-effect transistors (MESFETs) were fabricated by reactive dc sputtering of either Ag. Pt, Pd, and Au as Schottky gate contacts on ZnO thin films grown by pulsed-laser deposition on a-plane sapphire substrates. The individual properties and influences of the four gate metals on the performance of the MESFETs have been investigated. Pt- and Ag-gate MESFETs show excellent electric properties with on/off-ratios of 4.5 x 10(6) and 1.1 x 10(8), respectively, and low off-currents in the picoampere range. The leakage currents for Pd- and Au-MESFETs are 2 and 4 orders of magnitude higher than for Ag. Maximum off-voltages of - 1.4 V have to be applied at the gate in order to fully close the n-type (normally-on) channels. Channel mobilities of 6.3,11.4,12.8, and 24 cm(2)/VS were observed for Ag, Pt, Pd, and Au, respectively. Studies of the device performance at elevated temperatures in the range between 25 degrees C and 150 degrees C revealed that the MESFETs are stable at least until 75 degrees C. An annealing effect, which improved the MESFETs electric properties, could be observed for Ag, Pt, and Au. (C) 2009 Elsevier B.V. All rights reserved.