The impact of surface passivation, barrier Al composition and heterointerface quality on the low frequency noise characteristics of AlGaN/GaN MODFETs is investigated. Despite the considerable variation of noise level and frequency exponent of the 1/f noise characteristics of different heterointerface quality devices, it is found that the drain noise current characteristics are independent of Al composition. The surface treatment of same heterointerface roughness devices is also found to have no influence. This observation, while excluding the drain noise current as a tool suitable for studying the surface conditions and barrier type of AlGaN/GaN MODFETs, suggests the possibility of conducting low frequency noise studies for investigating the quality of the heterointerface. (c) 2005 Elsevier Ltd. All rights reserved.