In this letter, an investigation of pseudomorphic Ga 0 25 Al 0 75 As/Ga 0 80 In 0 20 As/GaAs heterostructure insulatedgate FETs (HIGFET) for microwave power applications is presented. Devices have been fabricated using Au/WSi self-aligned gate technology with SiO 2 sidewalls. The fabrication process has been optimized in order to realize 0.3 m gate-length transistors with reduced short-channel effects and improved rf power performance. dc and rf extracted parameters let us expect very attractive capabilities: for N-type HIGFET, a current density of 460 mA/mm and an extrinsic transconductance of 480 mS/mm are obtained. Measurements at 10 GHz using load-pull power setup have been carried out: 300 mW/mm maximum output power, 14 dB linear gain, and 65% PAE, for low (3 V) value. From our knowledge, these power results are the first reported for 0.3 m-HIGFETs.