The osmotic energy, as a representative of sustainable clean energy, has provided promising strategies to the energy shortage and the environmental pollution. Via selectively diffusing (cations or anions) through the porous membrane, the osmotic energy can be converted into electricity directly. Nevertheless, the energy-conversion efficiency is significantly limited in the lower surface charge at the membrane surface. In response, here a novel gate-controlled nanopore (field effect transistor-like) as an efficient osmotic generator is exploited. With real-time application of negative gate voltages, the surface charge density is accurately enhanced by an order of magnitude from −0.01 to −0.1 C m⁻² while maintaining an effective salinity difference. Based on that, the single-pore osmotic power is amazingly boosted by four orders of magnitude, reaching the summit of 2.90 nW, which outperforms the state-of-the-art 2D system represented by single-layer MoS₂ of 1 nW. Further expanding into porous membranes, the corresponding power density reaches the pioneering of 1008 W m⁻², far more exceeding the commercial standard of 5 W m⁻². Obviously, this work gives an underlying insight into ionic transport in confined nanochannels, as well as providing an alternative template for efficient osmotic energy generation.