  We report on the broadband THz response of InGaAs/GaAs HEMTs operating at
1.63 THz and room temperature deep in the saturation regime. We demonstrate
that responses show linear increase with drain-to-source voltage (or drain bias
current) and reach very high values up to 170V/W. We also develop a
phenomenological theory valid both in the ohmic and in the saturation regimes.
