Acousto-optic (AO) devices based on surface acoustic wave (SAW) propagation are widely studied for signal processing and optical computing systems. Among them, devices formed by a multilayer acoustic structure of III/V semiconductor materials are of particular interest because of the acoustic dispersion characteristics, which increase the number of design parameters to be used. In this paper, we present an accurate model of the acousto-optic interaction in III/V multilayer guiding structures having N layers of different materials, taking into account electro-mechanical and optical losses. By considering the full SAW field distribution, we calculate the overlapping integrals of diffracted modes in the grating region and compare the results in terms of diffraction efficiency with a well-known approximated design expression. A number of different cases have been analyzed, concerning proton exchanged and titanium indiffused lithium niobate waveguides and III/V semiconductor guiding structures, such as ZnO/AlGaAs/AlGaAs. The AO transducer behavior is defined in terms of diffraction efficiency as a function of the acoustic frequency and geometric parameters. The typical behavior of Bragg-regime diffraction in acoustooptic cells on LiNbO3 and GaAs planar waveguides has been confirmed, when both +1 diffraction order and higher orders are produced by the acoustooptic grating as output guided modes. Interesting diffraction properties have been derived as a function of waveguide structure, transducer acoustic power, grating length and applied acoustic frequency.