In order to establish the general way to prepare thin film crystals of organic semiconductors, we studied annealing effects on the heteroepitaxial growth of Cu-phthalocyanine (CuPc) crystallites on KCl {0 0 1} substrate crystals. CuPc was deposited on a cleaved KCl. single crystal by vacuum evaporation (under 10(-4)Torr). Then, the sample was taken out from the vacuum chamber and annealed in the air. On the CuPc as-deposited surface, no clear contrast was observed by scanning electron microscopy (SEM). On the contrary, many needle-like crystallites could be observed after the annealing treatment. Those crystallites were oriented so that their long axis was parallel to the <1 0 0> direction of the KCl substrate. We also investigated the effects of the annealing temperature and annealing duration time to find an optimal annealing condition. (C) 2003 Elsevier Science B.V. All rights reserved.