In GaAs‐GaAsP strained‐layer superlattices grown lattice matched to GaAs are effective buffer layers in reducing dislocations in epitaxial GaAs films grown on Si substrates. The strained‐layer superlattice structure permits high values of strain to be employed without the strained‐layer superlattice generating dislocations of its own. We find that the strained‐layer superlattice buffer is extremely effective in blocking threading dislocations of low density and is less effective when the dislocation is high. It appears that for a given strained‐layer superlattice there is a finite capacity for blocking dislocations. Transmission electron microscopy has been used to investigate the role of the superlattice buffer layer.