By Monte Carlo simulations we investigate the plasma spectrum in n-type InGaAs field effect transistors at 300 K in the whole region of operating conditions from ohmic to saturation regime of the transconductance characteristics. The presence of a two dimensional (2D) plasma peak predicted within the gradual channel approximation is confirmed by the microscopic model and its properties are analyzed systematically. At the highest gate voltages the 2D peak is found to become practically independent of the channel width. (C) 2010 Elsevier Ltd. All rights reserved.