Poly(ethylene terephthalate) samples were implanted to 100 keV Ar+ ions at room temperature at fluence ranging from 1x1015 cm-2 to 2x1016 cm-2. Surface DC electrical conductivity was found to be enhanced with increase in ion fluence. The energy deposited per unit path length per ion (LET) has been found to be the most important parameter responsible for the observed changes. The formation of a highly cross-linked hydrogenated amorphous carbon structure in the implanted layer of PET was confirmed though Raman spectroscopy. This carbonaceous structure, made of conjugated double or triple bonds, was found responsible for the observed electrical and structural changes in argon implanted PET.