A low insertion loss single-pole-single-throw (SPST) pseudomorphic high electron mobility transistor (pHEMT) switch utilizing the n(+)-type doping in AlAs etching stop layer was fabricated and investigated. This novel design reduces device sheet resistance resulting in an improvement of dc and rf power performance. In addition, the gate recess selectivity for GaAs/AlAs interface was not sacrificed after highly n(+)-type doping in AlAs etching stop layer. The pHEMT with n(+)-AlAs etching stop layer, also named Modified pHEMT (M-pHEMT), demonstrated a lower sheet resistance (R-sh) of 65.9 Omega/gamma, a higher maximum drain-to-source current (I-dmax) of 317.8 mA/mm and a higher peak transconductance (g(m)) of 259.3 mS/mm which are superior to standard pHEMT performance with values of 71.9 Omega/gamma, 290.3 mA/mm and 252.1 mS/mm, respectively. Due to a significant sheet resistance improvement from this novel epitaxial design, an SPST pHEMT switch was realized to manifest its industrial application potential. The results achieved an on-state insertion loss of 1.42 dB, an off-state isolation of 13.02 dB at 0.9 GHz, which were superior to traditional pHEMT switch under same condition of operation with values of 1.68 dB and 11.42 dB, respectively. It is proved that dual n(+)-doping AlAs etching stop layers scheme is beneficial for low loss microwave switches applications. (C) 2009 Elsevier Ltd. All rights reserved.