We report a simple and inexpensive way for the preparation of highly transparent ZnO thin films and their application as active layer in UV ray sensor devices. ZnO thin films were deposited on glass substrates by thermal evaporation of pure ZnO powder. The as-deposited films were then annealed at different temperatures (100, 200, 300 and 400 degrees C) for various time durations (5, 15,25 and 35 min) to make optically transparent in the visible region. The films annealed at 300 degrees C for 15 min show very good visible transparency and other material properties. These films were used as the active material for Ag/ZnO/Ag UV sensor devices. The sensor devices are photo conductive type and only sensitive in the UV region of the electromagnetic spectrum. Maximum photo-current gain of the UV sensor device is similar to 2. Possible sensing mechanism has been discussed. (C) 2012 Elsevier Ltd. All rights reserved.