The low frequency noise of AlGaN/GaN transmission line model (TLM) structures has been investigated in a wide temperature range. Deviation of low frequency noise from 1/f dependence has been observed. The results indicate that the structure become more non-linear upon increasing of power. The observed features have been explained as a result of non-equilibrium condition in TLM structures, equilibrium and non-equilibrium noise cases have been studied. The non-equilibrium fluctuations in gateless TLM structures were analysed taking into account the influence of the positive surface charge, formed by polarization effects on dynamics of non-uniform potential redistribution along the channel. (C) 2004 Elsevier B.V. All rights reserved.