CuPt‐type ordering in off‐stoichiometric III‐V semiconductor alloys has been investigated by a Monte Carlo method based on an Ising‐like crystal growth model for the layer‐by‐layer stacking on a (001) substrate. (110) Fourier power spectra of the atom configurations thus obtained exhibit superlattice spots due to the CuPt ordering. In the (11¯0) spectra, satellite reflections arise, flanking the fundamental lattice spots of the zinc‐blende structure and their intensity increases with the progress of ordering. The results are in good agreement with the experimental results previously obtained by transmission electron microscopy. The calculated atomic arrangement confirmed that the compositional modulation is the cause of the satellite reflections along the [110] direction. ©1995 American Institute of Physics.