© 2014 Elsevier B.V. All rights reserved. This work focuses on the study of zinc sulfide (ZnS) thin films prepared by chemical bath deposition. The effect of the pH ranging from 10.0 to 10.75 on quality of ZnS thin films on SiO2 substrate is investigated. The effect of pH on the surface showed that the variation of pH has a significant effect on the morphology of the ZnS thin films. The sample with pH value of 10.50 was uniform, free of agglomerates with band gap energy about 3.67 eV. The resistivity of ZnS thin films on SiO2 substrate with different pH value were about 107 ω cm.