High-mobility strained Ge0.958Sn0.042 p-channel metal-oxide-semiconductor field-effect-transistors (p-MOSFETs) with ammonium sulfide [(NH4)(2)S] surface passivation were demonstrated. A similar to 10 nm thick fully-strained single crystalline GeSn layer was epitaxially grown on Ge (1 0 0) substrate as the channel layer. (NH4)(2)S surface passivation was performed for the GeSn surface, followed by gate stack formation. Ge0.958Sn0.042 p-MOSFETs with (NH4)(2)S passivation show decent electrical characteristics and a peak effective mobility of 509 cm(2)/V s, which is the highest reported peak mobility obtained for GeSn channel p-MOSFETs so far. (c) 2013 Elsevier Ltd. All rights reserved.