An accurate distributed model of field effect transistors, including the parasitic impedances of the electrodes and the mutual coupling between them for analyzing the propagation effects along the electrodes working at millimeter wave frequencies, is presented. A numerical method is used to calculate the S-parameters of the distributed model. Then, a corresponding simpler semidistributed model, which avoids solving coupled differential equations, is then presented. A GaAs pHEMT example is given to show the well agreement of the S-parameters of the measurement and the distributed model ranging from 1 to 60 GHz. The S-parameters of the semidistributed model agree well with that of the distributed model up to 100 GHz, and both of the models can be applied for S-parameters prediction out of the measurement equipment range. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.