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The effects of recess etch in alloyed ohmic contacts have been studied on InAl(Ga)N/AlN/GaN high-electron-mobility transistors (HEMTs) using a Si-containing ohmic metal stack. The optimized contact resistance is as low as 0.23 Ω mm. With decent ohmic contacts, an In0.13Al0.83Ga0.04N barrier HEMT with a 66-nm long gate and dielectric-free passivation followed by a 5 nm Al2O3 deposition, shows a maximum drain current density Idmax of 2.3 A/mm, a peak extrinsic transconductance gmext of 560 mS/mm and a current gain cut-off frequency fT of 210 GHz, which are among the highest reported values in quaternary InAlGaN/AlN/GaN HEMTs.