Herein, we report a triboelectric nanogenerator (TENG) with improved performance using extremely-long sub-50 nm grating patterns with high aspect ratio (4,000,000: 1) fabricated by the multistep pattern downscaling (MS-PaD) method, which is advantageous in terms of fast throughput, high resolution, cost-effectiveness, industrial compatibility, and large-area scalability in nanofabrication. The intensely-arrayed nanograting pattern is replicated to the flexible substrate on the 8-in. wafer-scale without any defects for the nanograting-assisted TENG (NGTENG). As the well-aligned nanoscale morphology in sub-50 nm grating leads to efficient triboelectric charges, the NGTENG shows an outstanding performance enhancement by a factor of 200 compared to non-patterned surface during repetitive contact electrification. To demonstrate capability of self-powered electronics, the output power from the NGTENG is directly used for charging a commercial capacitor and turning on the LEDs. In addition, theoretical study of triboelectric signals according to nanoscale-tuned metal electrodes were investigated to improve the effective output and robustness of triboelectric device.