Kink effects in an In-rich InxGa1-xAs (x=0.53–0.63) linearly graded channel of an In0.45Al0.55As/InxGa1-xAs metamorphic high-electron-mobility transistor have been effectively relieved by depositing a high-barrier Ni/Au gate with the silicon nitride passivation. Complete physical investigations for the relieved kink effects have been made by comparing identical devices with/without a high-barrier Schottky gate or the surface passivation. After successfully suppressing the kink effects, the proposed device has shown a superior voltage gain of 173.8, low output conductance of 2.09 mS/mm, and excellent power-added efficiency of 54.1% with high output power (power gain) of 14.87 dBm (14.53 dB). Improved linearity and excellent thermal threshold coefficient (∂Vth/∂T) of -0.14 mV/K have also been achieved. The proposed design provides good potential for high-gain and high-linearity circuit applications.