The　adsorption　and　decomposition　of　ethanethiol　on　GaN　(0　0　0　1)　surface　have　been　investigated　with　first-principles　calculations.　The　DFT　calculations　reveal　that　ethanethiol　adsorbs　dissociatively　on　the　clean　GaN　(0　0　0　1)　surface　to　form　ethanethiolate　and　hydrogen　species.　An　up　limit　coverage　of　0.33　for　ethanethiolate　monolayer　on　GaN　(0　0　0　1)　surface　is　obtained　and　the　position　of　the　sulfur　atom　and　the　tilt　angle　of　the　thiolate　chain　are　found　to　be　very　sensitive　to　the　surface　coverage.　Furthermore,　the　reactivity　of　ethanethiol　adsorption　and　further　thermal　decomposition　reactions　on　GaN　(0　0　0　1)　surface　is　discussed　by　calculating　the　possible　reaction　pathways　and　ethene　is　found　to　be　the　major　product.　©　2008　Elsevier　B.V.　All　rights　reserved.