A simple equivalent circuit model including noise sources for the GaN heterostructure field effect transistor is presented and analyzed. The model is used to determine optimum source impedance for low noise amplifier applications. A good agreement between the model and measured NFmin of experimental devices is shown. Prototype transistors with a 0.75 mu m gate length and 80 mu m width delivered a power-added efficiency of 45.6% and a minimum noise figure of 2.1 dB at 2.4 GHz when operated from a 48 V supply. Gate leakage current was found to be an important noise source. (c) 2006 American Vacuum Society.