Using Kane's 8-band k (.) p theory and the envelope function approximation we derive a tight binding Hamiltonian for III-V semiconductor quantum well structures, which accurately models band structure and spin-orbit coupling. By applying a potential difference across the well we have calculated the Rashba spin-splitting in the lowest conduction subband. For identical well widths the Rashba splitting in InSb is shown to be approximately twice that of InAs and, in all cases, passes through a weak maximum with increasing quasimomentum. (C) 2003 Elsevier B.V. All rights reserved.