The selenization of co-evaporated Cu-In layers in Se/N-2 gas mixture at atmospheric pressure was investigated by in situ resistivity measurements. For selenization processes and in situ measurements a special container (a quasi-closed system) with mechanical contacts to the selenized film was constructed. The total resistance of the metallic layers and the contact system was approximately 10 Omega before the reaction starts. During the selenization processes it increases to more than 10 kOmega, indicating the conversion of metals into CuInSe2 The resistivity curve indicates the start and end point of the chemical reactions and identifies three different stages of conversion. An interpretation of the in situ resistivity measurements in accordance with structural investigations of selenized layers at different selenization stages is presented. (C) 2003 Elsevier B.V. All rights reserved.