Abstract We have demonstrated 50-nm enhancement-mode (E-mode) In0.7Ga0.3As PHEMTs with fmax in excess of 1 THz. The devices feature a Pt gate sinking process to effectively thin down the In0.52Al0.48As barrier layer, together with a two-step recess process. The fabricated device with Lg = 50-nm exhibits VT = 0.1 V, gm,max = 1.75 mS/μm, fT = 465 GHz and fmax = 1.06 THz at a moderate value of VDS = 0.75 V. In addition, we have physically modeled the abnormal peaky behavior in Mason’s unilateral gain (Ug) at high values of VDS. A revised small signal model that includes a shunting Rgd-NDR with negative value successfully describes the behavior of the device from 1 to 67 GHz. .