The influence of high temperature (over the melting point) annealing on the properties of poly (3-hexylthiophene) (P3HT) films had been investigated. By comparing the films with different annealing temperature, we found that P3HT films annealed at 260 degrees C is similar to amorphous melting process, although it had the highest crystallinity. The film thickness was increased after annealing at 260 degrees C which suggested that there were a large number of 'micro-pores' in the films. Since the P3HT backbone around the micro-pores was in a nearly free state (easy to rotate and bend), the samples annealed at 260 degrees C would exhibit a similar 'melting' behavior at low temperature (below 180 degrees C) with the highest crystallinity. (C) 2015 Elsevier B.V. All rights reserved.