CdS thin films deposited from chemical bath containing citratocadmium(II) and thiourea are intrinsic and highly photosensitive. In the present letter, we discuss the conversion of such films tontype by thermal diffusion of indium from an evaporated 50 nm indium film deposited on the CdS thin film. The process which takes place in the temperature range of 250 °C–350 °C involves the formation of an In2O3surface layer which acts as a barrier preventing the outdiffusion of indium. This allows indium to diffuse into the CdS film and results in an indium‐doped CdS thin film. The electrical conductivity of such films is about 300 &OHgr;−1 cm−1. All beneficial optical properties of chemically deposited CdS thin films for application as a window material in heterojunction optoelectronic devices are retained. ©1995 American Institute of Physics.