Electrical conductivity of non-stoichiometric copper selenide thin films of different phases prepared using chemical bath deposition was examined in the temperature range 10 to 500 K. Samples showed phase transitions at 45 and 450 K attributed to copper deficiency or excess of selenium in copper selenide samples arising during the preparation. A prominent defect level was also detected at 250 K; such effect vanishes upon annealing and is attributed to copper vacancy. Conductivity measurements also confirmed phase transformation of Cu3Se2 phase to Cu2-xSe at 413 K. (C) 2004 Elsevier B.V. All rights reserved.