eries of poly(ethylene terephthalate)(PET) films with different degree of planar orientation [△(xy)z] were prepared by drawing biakially in different stretching ratio. It was found that the depth of discrete trapping levels increased with the rise of △ (xy)z according to the investigations of thermally stimulated current. Due to the changes of conformation and orientation structot of molecular chains

the kinds 'of structural defects increased which caused the number of discrete trapping levels to increase from 2 of amorphous to 6 of specimen T-1 and the distribution width of depth of discrtet trapping levels to broaden from 0.05eV of amorphous to 0.2eV of specimen B-1.