In this paper, we present the study, the realisation and the measurement of an amplifier at 900 MHz using the Doherty technique. This technique is based on the large signal performance analysis of the active devices under different drive levels. The improvements made by the application of this technique were checked by simulations and measurements on a prototype made with two MESFETs transistors. For a 6 dB backoff, obtaining significant values of Power Added Efficiency was possible thanks to the application of a methodology of design, specific to this technique.