The thermal equilibrium concentrations of the six electrically neutral single point defect species in GaAs are expressed as explicit functions of well-defined thermodynamic quantities. The difference between the Gibbs free energies of an arsenic atom in the interior of a GaAs crystal and in an arsenic vapor phase molecule is emphasized. Numerical values of the thermal equilibrium concentrations of the gallium and arsenic vacancies and the two antisite defects are estimated. It is of interest that the calculated thermal equilibrium concentration of the anion antisite defect AsGa0 reaches a peak value of about 1 × 1017 cm-3 and is almost temperature independent. This computed value for AsGa0 is consistent with experimental findings. © 1991.