Excellent triboelectric and mechanical properties are achieved on the same material for the first time by developing an effective, general, straightforward, and area-scalable approach to surface modification of a polyethylene terephthalate (PET) film via inductive-coupled plasma etching. The modification enables gigantic enhancement of triboelectric charge density on the PET surface. Based on the modified PET as a contact material, a triboelectric nanogenerator (TENG) exhibits significantly promoted electric output compared to the one without the modification. The obtained electric output is even superior to a TENG made of conventional polytetrafluoroethylene that is known for its strongest ability of being charged by triboelectrification among all engineering plastics. Detailed characterizations reveal that the enhancement of triboelectric charge density on the PET is attributed to both chemical modification of fluorination and physical modification of roughened morphology in nanoscale. Therefore, this work proposes a new route to obtaining high-performance TENGs by manipulating and modifying surface properties of materials.