200nm gate-length power InAlAs/InGaAs MHEMTs with T-shaped gate are characterized for DC, RF, and power performance. The MHEMTs show excellent DC output characteristics with an extrinsic transconductance of 510mS/ mm and a threshold voltage of - 1.8V. The fT and fmax obtained for the 0.2μm × 100μm MHEMTs are 138 and 78GHz, respectively. Power characteristics are obtained under different frequencies. When input power （Pin） is - 0. 88dBm （or 2. 11dBm）,the MHEMTs exhibit high power characteristics at 8GHz. Output power （Pout） ,associated gain, power added efficiency （PAE） and density of Pout are 4. 05（13.79）dBm,14. 9（11.68）dB,67. 74（75.1）% ,254（239）mW/mm respectively. These promising results are on the path to the application of millimeter wave devices and integrated circuits with improved manufacturability over InP HEMT.
