The interdiffusion of lattice-matched InP/(In,Ga)As superlattice structures (nominally undoped, p-doped and n-doped) has been studied by analytical electron microscopy (x-ray analysis) using a field emission gun, scanning transmission electron microscope. The point-spread function of the electron beam was used to correct the experimental data (obtained as x-ray maps, 50×50 nm in area) in order to derive diffusion profiles of the group V elements (As, P) after annealing. The results, showing a marked asymmetry in the As profiles after annealing, are interpreted using a model based on the coherent diffusion of the group III and V elements on their own sublattices, each of which is treated as a regular solution. A mathematical procedure, based on the minimization of the difference between the measured and predicted concentration profiles, is employed to compute the two lattice-specific composition-dependent velocities from the experimental diffusion profiles. A good agreement is found between the experimental measurements and the predictions of the model. The role of coherency strains in the interdiffusion process is discussed. © 2002 American Institute of Physics.