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A high breakdown voltage and a high turn-on voltage (Al0.3Ga0.7)0.5In0.5P/InGaAs quasi-enhancement-mode (E-mode) pseudomorphic HEMT (pHEMTs) with field-plate (FP) process is reported for the first time. Between gate and drain terminal, the transistor has a FP metal of 1 μm, which is connected to a source terminal. The fabricated 0.5×150 μm2 device can be operated with gate voltage up to 1.6 V owing to its high Schottky turn-on voltage (VON=0.85 V), which corresponds to a high drain-to-source current (Ids) of 420 mA/mm when drain-to-source voltage (Vds) is 3.5 V. By adopting the FP technology and large barrier height (Al0.3Ga0.7)0.5In0.5P layer design, the device achieved a high breakdown voltage of -47 V. The measured maximum transconductance, current gain cutoff frequency and maximum oscillation frequency are 370 mS/mm, 22 GHz , and 85 GHz, respectively. Under 5.2-GHz operation, a 15.2 dBm (220 mW/mm) and a 17.8 dBm (405 mW/mm) saturated output power can be achieved when drain voltage are 3.5 and 20 V. These characteristics demonstrate that the field-plated (Al0.3Ga0.7)0.5In0.5P E-mode pHEMTs have great potential for microwave power device applications.