Measurements of critical layer thicknesses and strain relaxation have been made for AlSb on GaSb(001) using ion scattering/particle induced x‐ray techniques. The maximum strain in the films agrees well with that calculated from bulk elasticity data. The critical thickness as measured by the ion channeling experiment is ≊140±30 Å. Films exceeding the critical thickness do not relieve the strain immediately but rather show a gradual relaxation up to ≊1000 Å. The results are compared with theoretical models of strain relief and critical thickness. Issues related to the protection of the AlSb films from oxidation, beam damage, and the use of particle‐induced x‐ray emission have been addressed. A protective cap of ≊200 Å of Be was found to give the best performance.