The production and annealing of radiation damage in GaSb Ne‐implanted at high energy are studied by transmission electron microscopy and Rutherford backscattering spectrometry in combination with the channeling technique. The anomalous swelling phenomenon of implanted GaSb, previously reported, is found to be related to the formation of voids and microtwins in the crystalline implanted layer. These defects appear when the introduced damage exceeds a critical amount and lead to the formation of a porous polycrystalline GaSb layer, whereas in most other III‐V materials an amorphous layer is formed. Provided the swelling is avoided, there is a good recovery of the lattice upon rapid thermal annealing at 600 °C. Otherwise, a heavily perturbed layer remains, containing voids, dislocations and, at sufficiently high doses, polycrystalline GaSb. From previously published results, it is inferred that the InSb behavior towards radiation damage is similar to that of GaSb.