Poly(ethylene terephthalate) (PET) films were obtained by cold crystallization. Samples with different crystallinities were produced by annealing amorphous samples at different temperatures and for different times. The structural organization was analyzed by x-ray, density, transport properties, and Fourier-transform infrared measurements. The presence of trans conformer is associated with the appearance in the infrared spectrum of a band at about 973 cm−1. A correlation between the intensity of this band and the structural order of different semicrystalline PET films was proposed. Assuming that the fraction of the amorphous component (αa) can be determined from the sorption measurements, at low dichlorometh-ane activity, the fraction of the ordered phase (1-αa) could be correlated with the intensity of the infrared band at 973 cm−1. The result was consistently found to be higher than the fraction of crystalline phase derived from x rays and density measurements. This led to the suggestion that in these samples, besides the crystalline phase, there is also a fraction of a mesomorphic phase, impermeable to dichloromethane at low activity.