Mechanisms of photocarrier generation in poly(ethylene terephthalate) (PET) have been investigated. In the wavelength range of λ ≦320 nm, the photocurrent spectra correspond closely with the optical absorption spectra of PET and the assignment of the absorption peaks revealed that photocarriers are generated through ππ* excitations. In the wavelength range from 320 to 400 nm, photocarriers are injected from metal electrodes. The threshold energies for Al and Cu electrodes are 2.87 and 2.94 eV, respectively, indicating the presence of surface states. The simplified model gives the density of the surface states as 1.7 × 1014 cm−2 eV−1.