The temperature-dependent characteristics of AlGaN/GaN lateral field-effect rectifiers (L-FER) are studied in detail by investigating the dependence of forward and reverse characteristics on the device geometry (Schottky-gate-controlled channel) and temperature. The forward current increased with the decrease of channel length, while the specific on-resistance showed a positive temperature coefficient. Moreover, different temperature-dependent reverse characteristics were observed for the L-FERs with different device geometries. A combination of impact ionization in the Schottky-gate-controlled channel and the Schottky reverse leakage current is applied to understand the reverse breakdown of L-FER.