We present the device and integrated circuit (IC) characteristics of GaAs metamorphic high electron mobility transistors (MHEMT). A 0.15×100㎟ MHEMT device shows a drain saturation current of 480 mA/㎜, an extrinsic transconductance of 830 mS/㎜, and a threshold voltage of-0.65 V. The obtained cut-off frequency and maximum frequency of oscillation are 141 and 243 GHz, respectively. The noise performance is excellent; minimum noise figures of 0.79 and 0.64 dB, and associated gains of 10.56 and 12.4 dB at 26 GHz for 0.15 ㎜-long T-gate and 0.1 ㎜-long G-gate power MHEMTs, respectively, with In content of 53% in InGaAs channel. Using the MHEMT technology with a 0.15 ㎜-long T-gate, we designed and fabricated monolithic microwave integrated circuits (MMICs) on 4-inch MHEMT wafers. The MMIC performance for a power amplifier and a down mixer for 76-77 GHz band is presented. These devices and ICs can be used for wireless telecommunications systems and also in millimeter-wave sensor systems for commercial or military applications.