We employ an ab initio time-dependent Hartree-Fock (TDHF) formalism combined with sum-over-states (SOS) method to calculate the linear and nonlinear optical properties of direct semiconductor clusters. The obtained electronic absorption spectra predict a variety of the spectral shapes and peak positions and an increase of the second-order nonlinear optical response with an increase of V-group ionic radius in the title clusters. Charge transfers from the pi bonding to pi antibonding orbitals between III and V group atoms make a significant contribution to the second-order polarizability. (C) 2003 Elsevier Science B.V. All rights reserved.