We evaluated the thermal crystallization of deposited films made of 2,5-bis(4-biphenylyl)thiophene (BP1T) and 1,4-bis(5-phenylthiophen-2-yl)benzene (AC5), which are thiophene/phenylene co-oligomers (TPCOs). The deposited films of both BP1T and AC5 showed a microcrystalline phase, and initial microcrystals grew 10- 100 times with thermal treatment. The XRD profile of BP1T indicated that the thermal treatment resulted in a densely packed crystalline layer, and the XRD results for AC5 after treatment were similar to those reported for AC5 single crystals. Thermal treatment of the deposited film is an effective process to grow microcrystals of deposited films of TPCO. We inferred that one of the main mechanisms of thermal crystallization involves the strain energy, which was saved around the grain boundaries. (c) 2012 Elsevier B.V. All rights reserved.