The solubility of both native point defects and dopants in semiconductors is dependent on growth temperature, on crystal stoichiometry and on Fermi level position. At high temperatures III-V compounds contain high concentrations of predominantly charged native point defects. Published titration and density/lattice parameter measurements on GaAs show conclusively that melt-grown crystals contain similar to10(19) cm(-3) As-vacancies and As-interstitials at the melting point. The arsenic vacancies form a relatively shallow (similar toE(c) - 0.1 eV) donor state. The concentration of these ionised vacancies at the melting point of GaAs, and under the conditions used for LPE growth from Ga-solution, exceeds the intrinsic electron-hole concentration. Hence, these ionised vacancies control the electro-neutrality of the crystal (and hence the position of the Fermi level) during growth under these conditions. The As vacancy concentration obtained from titration measurements, when inserted into a comprehensive equilibrium thermodynamic description of the system, accurately predicts the observed range of linear dopant solubility obtained for both Groups IV and VI donor dopants. The currently accepted hypothesis that this linear range is determined by a non-equilibrium incorporation process controlled by a Schottky barrier at the crystal/melt interface is therefore unnecessary. It is shown that donor and acceptor dopant incorporation, EL2 formation and annealing behaviour in GaAs can all be fully explained by the thermodynamic model. The differing doping behaviour exhibited by the various other zinc-blende III-V compounds is shown to be related to the differing relative numbers of native point defects on the two sub-lattices. (C) 2002 Elsevier Science B.V. All rights reserved.