Scaled AlGaN/GaN heterostructure field-effect transistors (HFETs) with a high unity current gain cut-off frequency (fT) and maximum oscillation frequency (fmax) were fabricated and characterised on an SiC substrate. In the device, the source-to-drain distance (Lsd) was scaled to 600 nm using regrown n+-GaN Ohmic contacts. In addition, a 60-nm T-shaped gate was fabricated by self-aligned-gate technology. A recorded drain saturation current density (Ids) of 2.0 A/mm at Vgs=2 V and a peak extrinsic transconductance (gm) of 608 mS/mm were obtained in the scaled AlGaN/GaN HFETs. Moreover, in the devices with a 60-nm T-shaped gate, the maximum values of fT and fmax reached 152 and 219 GHz, respectively.