DC, RF, and low-frequency noise characteristics of selectively hydrogen-pretreated Al0.24Ga0.76As/In0.2Ga0.8As double heterostructure pseudomorphic high electron mobility transistors (p-HEMTs) were investigated. The gate region of the p-HEMTs was exposed to a hydrogen plasma in a reactive ion etching chamber, followed by a thermal annealing, prior to a gate metallization. Strong dependence of the threshold voltage, the gate leakage current, and low-frequency noise characteristics on the RF power of the hydrogen plasma and the annealing temperature was observed. Control of the donor density in the selectively hydrogen-pretreated gate region produced a threshold voltage shift as large as 1 V, which was successfully used for a fabrication of enhancement/ depletion HEMTs (E/D-HEMTs). The selective hydrogen pretreatment (SHP) produced improved gate leakage current, breakdown voltage, and low-frequency characteristics. These results indicate the potential of the selective hydrogen pretreatment for use in an easy fabrication of E/D-HEMTs. (C) 2004 Elsevier Ltd. All rights reserved.