Multilayers composed of many thin layers of GaAs and GaAs0.5P0.5 were grown on GaAs substrates by chemical vapor deposition. They were examined by optical microscopy, electron microscopy and scanning electron microscopy. Slip lines, dislocation pile-ups, threading dislocations, and cracks were found. These defects were made to relieve elastic stresses generated as a result of misfit between the multilayer taken as a whole and its substrate. The roles of dislocation pile-ups and superkinks in the propagation of dislocations through multilayers are discussed. © 1975.