The dependence of Zn concentration, N Z n , upon Zn partial pressure, P Z n , has been measured in InP and In 0 . 5 3 Ga 0 . 4 7 As after organometallic vapor phase epitaxial growth and compared with the equilibrium Zn solubility under comparable conditions. It was found that the Zn concentration incorporated during growth of In 0 . 5 3 Ga 0 . 4 7 As follows the equilibrium solubility, i.e. N Z n P Z n 1 / 2 . However, it was found that the Zn concentration incorporated during growth of InP deviated from equilibrium, i.e. N Z n P Z n was measured, similar to what has been previously reported for GaAs. For both InP and In 0 . 5 3 Ga 0 . 4 7 As, the maximum Zn concentration was found to be consistent with previously measured Zn solubility limits. From these results, we conclude that at T=600 o C, (1) the Fermi energy at the surface of the InP is pinned below the intrinsic Fermi energy at a value of approximately E i -E f ~0.35 eV, i.e. E f is only modestly above the valence band edge, and (2) pinning of the Fermi energy at the surface of In 0 . 5 3 Ga 0 . 4 7 As could not be measured.