An enhancement-mode pseudomorphic high electron mobility transistor using optimum reactive ion etching (RIE) technology without damaging 2-D channel has been developed, at the first time. By using the optimum RIE recipe, the selectivity between GaAs and AlGaAs is more than 150. In addition, the maximum transconductance of the device with the dimension of 300 mum x 0.4 mum reaches 235 ms/mm at V-ds, = 1.4 V. Furthermore, at 12 GHz, the output power and gain can achieve 17.9 dBm and 14.03 dB respectively. Operating at 12 GHz, the noise figure at V-ds = 4 V is down to 0.65 dB which is comparable to low noise depletion-mode device. (C) 2002 Elsevier Science Ltd. All rights reserved.