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. (C) 2008 Elsevier B. V. All rights reserved.