We report direct current (DC) and microwave performance of a 50-nm gate length (L g) quaternary-based InAlGaN/GaN/AlGaN high-electron-mobility transistor (HEMT) on SiC substrate with SiN passivation and by using a Tgate. The proposed HEMT structure is simulated using industry-standard Synopsys Sentaurus technology computer-aided design (TCAD). The regrown n++ GaN source/drain ohmic contacts show a peak drain current density (I dmax) of 2.9 A/mm along with low on-resistance of 0.49 X mm. A record power gain cutoff frequency (f max) of 425 GHz along with current gain cutoff frequency (f t) of 310 GHz are obtained by the substantial reduction in the device's intrinsic and extrinsic parasitic resistances and capacitances. A very thin 7nm In 0.13 Al 0.83 Ga 0.04 N quaternary barrier with an AlGaN back-barrier structure effectively mitigates the short-channel effect with an improved breakdown voltage (V BR) of 38 V. The prominent DC and microwave characteristics of the proposed HEMT make it an appropriate candidate for nextgeneration high-power millimeter-wave electronics.