Scaled InAlN/GaN heterostructure field-effect transistors (HFETs) with high unity current gain cut-off frequency (fT) on sapphire substrate were fabricated and characterized. In this device, scaled source-to-drain distance (Lsd) of 600 nm was realized by metal organic chemical vapor deposition (MOCVD) based on regrow nonalloyed n+-GaN Ohmic contacts. Moreover, a 50 nm rectangular gate was fabricated by self-aligned-gate technology. A high drain saturation current density (Ids) of 2.11 A/mm @ Vgs= 1 V and a peak extrinsic transconductance (gm) of 609 mS/mm were achieved in the InAlN/GaN HFETs. In addition, from the small-signal RF measurements, the values of fT and maximum oscillation frequency (fmax) for the device with 50-nm rectangular gate were extrapolated to be 220 GHz and 48 GHz. To our best knowledge, the value of fT is the best reported one for InAlN/GaN HFETs in China.