Scaled InAlN/GaN heterostructure field-effect transistors (HFETs) with high unity current gain cut-off frequency (fT) were realized by employing nonalloyed regrown n+-GaN Ohmic contacts, in which the source-to-drain distance (Lsd) was scaled to 600 nm. By processing optimization of dry etching and n+-GaN regrowth, a low total Ohmic resistance of 0.16 Ω·mm is obtained, which is a recorded value regrown by metal organic chemical vapor deposition (MOCVD). A 34 nm rectangular gate was fabricated by self-aligned-gate technology. The electrical characteristics of the devices, especially for the RF characteristics, were improved greatly after the reduction of ohmic resistance and gate length. The fabricated InAlN/GaN HFETs show a low on resistance (Ron) of 041 Ω·mm and a high drain saturation current density of 2.14 A/mm at Vgs=1 V. Most of all, the device shows a high fT of 350 GHz, which is a recorded result reported for GaN-based HFETs in domestic.