In this research work, an alternative methodology to design radio frequency (RF) class-E amplifier is proposed and verified. The conventional design procedure starts with a switch idealization of the device and extraction of the output capacitance based on S parameter measurements. Since these ideal conditions lead to non-optimal values at microwave frequencies, an optimization procedure on these values, using a non-linear model of the device, has to be applied in order to obtain higher performance. Unlike this legacy procedure, the proposed method starts the design of the RF class E power amplifier with the non-linear model directly to determine a more representative value of the equivalent capacitance, and thereby considering all the non-ideal and non-linear features of the device. © 2008 IEEE.