Self‐diffusion in InSb was studied, using radiotracers and refined sectioning techniques. The diffusion coefficients of neither In nor Sb seemed to depend on the ambient Sb pressure. A few pits several microns in depth were found to develop during diffusion of both In and Sb in InSb. Radioactivity associated with these pits led to tails in the diffusion profiles. The In:Sb divacancy is proposed as the defect primarily responsible for self‐diffusion of both components in InSb. The activation energy for diffusion for both In and Sb was found to be 4.3 eV. This consisted of effective enthalpies of formation and motion for the divacancy of 3.2 eV and 1.1 eV, respectively. The enthalpy of formation of the single vacancies was estimated to be 1.76 eV. The pre‐exponentialsD0in the Arrhenius relation for diffusion of In and Sb were 1.76×1013and 3.1×1013cm2sec−1, respectively. These high values are attributed primarily to the large vibrational entropy contributions of a divacancy.