This work investigates the adsorption of a PTCDA (3,4,9,10-perylene tetracarboxylic dianhydride) monolayer on a 2 x 1 S-passivated GaAs(1 0 0) surface with density functional based tight binding (DFTB) calculations. The structure of the first monolayer is discussed within the restricted class of surface unit cells including a single PTCDA molecule, and the calculated current-voltage characteristics are used to predict the electronic transport properties of the hybrid system. (C) 2004 Elsevier B.V. All rights reserved.