Abstract: Because of the high electron mobility and two-dimensional electron gas concentration, InP based pseudomorphic high electron mobility transistors(PHEMTs) become one of the most promising three-terminal devices which can operate in terahertz. The InAs composite channel was used to improve the operating frequency of the devices. The two-dimensional electron gas(2DEG) showed a mobility of 13000 cm2/(Vs) at room temperature. 70 nm gate-length InAs/In0.53Ga0.47As InP-based PHEMTs were successfully fabricated with two fingers 30 m total gate width and source-drain space of 2 m. The T-shaped gate with a stem height of 210 nm was fabricated to minimize parasitic capacitance. The fabricated devices exhibited a maximum drain current density of 1440 mA/mm(VGS=0.4 V) and a maximum transconductance of 2230 mS/mm. The current gain cutoff frequency fT and the maximum oscillation frequency fmax were 280 and 640 GHz, respectively. These performances make the device well-suited for millimeter wave or terahertz wave applications.