The measurement of impurity concentration in compound semiconductors reaches extremely high sensitivity. On the contrary, the methods for off-stoichiometry determination in II-VI crystals are not satisfactory. Some of the authors developed (in the past) a method for determining the off-stoichiometry in CdTe crystals measuring the high-temperature optical densities of vapors in equilibrium with solid samples. Thanks to accurate calibrations, the partial pressure of the vapor/solid systems could be derived and exploited to evaluate the sample off-stoichiometry. In the present work, the calibration procedures are shown for the determination of partial pressure for sulfides and selenides. The off-stoichiometry is derived for ZnTe, US and CdSe samples and the method effectiveness is confirmed. (c) 2007 Elsevier B.V. All rights reserved.