ZnTe 1Ϫx S x epitaxial layers grown on GaAs by molecular-beam epitaxy were studied by photoluminescence ͑PL͒ as a function of temperatures, excitation powers, and hydrostatic pressures. A sulfur-related emission peak, labeled as P 2 , is identified as a deep-level emission by hydrostatic-pressure PL measurement. This indicates that sulfur atoms form isoelectronic centers in a ZnTe matrix. The results qualitatively agree with the theoretical prediction and show experimental evidence of isoelectronic S in ZnTe. A model is proposed to explain the emission mechanisms in the ZnTe 1Ϫx S x system with small x values. ͓S0163-1829͑97͒01816-X͔