Because of the high valence electron density in Si- and GaAs-type semiconductors, their vacancies may be treated as macroscopic cavities. With this model one may calculate the divacancy binding enthalpy very simply in terms primarily of the reduction in cavity surface areas and secondarily, in the number of dangling bonds. The calculated value for Si is 0.9 eV which agrees with an empirical estimate of 0.9 eV obtained from measurements of the activation energy for divacancy migration and reorientation obtained by Cheng, Corelli, Corbett, and Watkins. Calculated values are also presented for 20 other IV-IV, III-V, and II-VI semiconductors where experimental values are not known to the author. © 1975 The American Physical Society.