A semiconductor-based tribovoltaic nanogenerator (TVNG) is a promising continuous direct current (DC) technology. However, the limited built-in/interfacial electric field causes unsatisfactory carrier separation and extraction efficiency and produces suboptimal and erratic output voltage, which is the major bottleneck that impedes further practical applications of TVNGs. Herein, we propose a novel insulator-based quasi-TVNG (I-Q-TVNG) with ultrahigh voltage and power profiting from the dramatically elevated interfacial electric field (tribo-bias). The outstanding quasi-tribovoltaic effect dominates the efficiently directional charge deposition and extraction rely on the extreme property of the insulator, including the inferior charge confinement capability of highly conductive insulator and the strong tribo-bias on high dielectric electret, thereby generating high-performance DC output. Meanwhile, synergistic strategies of increasing charge deposition and suppressing charge recombination can evidently enhance the charge extraction efficiency, facilitating the optimized I-Q-TVNG achieved a record-breaking DC output voltage (∼2324 V) and average power (∼11.2 mW), surpassing previous centimeter-level TVNGs by 16.8 times and 8.8 times, respectively. In addition, the device exhibits excellent stability (crest factor ∼1.0204) and durability (∼97.8% performance retention over 72 000 cycles). This work provides crucial insights into the dynamic behavior of induced charges by tribo-bias, and pioneers a fire-new avenue for developing high-voltage TVNGs towards practical applications.