The degradation of electrical characteristics of GaAs metal semiconductor field effect transistors (MESFETs) and heterojunction bipolar transistors (HBTs) can occur during plasma enhanced chemical vapor deposition (PECVD) of SiNX passivation films through the hydrogen passivation of dopants or creation of deep traps by ion bombardment or preferential loss of As. In this paper we report in the de characteristics of MESFETs and HBTs deposited with SiNX. using deuterated precursors (SiD4/ND3). For the MESFETs, changes in I-DS, g(m) and channel sheet resistance were typically 25%, with process pressure being the most important parameter, For the HBTs, changes in beta and sheet resistance of the base and emitter layers were again typically 15% for the conditions we investigated. (C) 2002 Published by Elsevier Science Ltd.