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A δ-doped In0.425Al0.575As/ InGaAs metamorphic high electron mobility transistor (MHEMT) has been fabricated successfully and demonstrated. The In0.425Al0.575As Schottky layer provides good breakdown voltage due to larger energy-gap than that of In0.52Al0.48As. Experimentally, a high extrinsic transconductance of 277 mS/mm with VDS = 2 V and a high drain-source saturation current density of 484 mA/mm with VGS =0 V are obtained for a 0.65×200 μm2 device at 300 K. Due to good carrier confinement in the channel layer, good pinch-off characteristic can be achieved. The measured fT and fmax for a 0.65 μm gate device are 60.5 and 108.5 GHz at VDS = 2 V and VGS = -1.5V. The NFminis 0.93 dB at 2.4 GHz, and the associated gain is 23.1 dB.