This letter reports on AlGaN/GaN high-electron-mobility transistors (HEMTs) on high-resistive silicon substrate with a record maximum oscillation cutoff frequency F _MAX . Double-T-shaped gates are associated with an optimized technology to enable high-efficiency 2-D electron gas control while mitigating the parasitic resistances. Good results ogate-length HEMTf F _MAX = 206 GHz and FT = 100 GHz are obtained for a 90-nm gate-length HEMT with 0.25-μm source-to-gate spacing. The associated peak extrinsic transconductance value is as high as 440 mS·mm ^-1 . To the authors' knowledge, the obtained F _MAX and Gm _ext are the highest reported values for GaN HEMTs technology on silicon substrate. The accuracy of the cutoff frequency values is checked by small-signal modeling based on extracted S-parameters.