This article presents the design of a monolithic high power amplifier with 4 W output power in the 16 GHz band (2.5 octave).The amplifier uses two gain stages composed by four and eight transistors. Power united monolithic semiconductor PPH25x process, on GaAs substrate with 70 mu m thickness, has been used. The Montecarlo analysis shows a small-signal gain's average value of 24 dB and output power levels higher than 36 dBm. (c) 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 54:27472751, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.2720