In this communication, we report a significantly high UV sensitivity of polycrystalline zinc selenide thin films prepared by chemical bath deposition technique. A three order of magnitude of photo current to dark current ratio is obtained for the as-deposited film under UV exposure. However, the photosensivity is found to decrease sharply upon open air isochronal annealing of the sample. The variation of the photocurrent to dark current ratio with annealing temperature is attributed to shrinking diameter of nano-wire like structures exhibited by the films, variation of the band gap energy and a decrease in the grain boundary charge density of the material which collectively enhance the free carrier concentration in the band leading to a substantial loss in the photosensitivity of annealed films compared to the as-deposited film. © 2018 Elsevier B.V.