The electric double layer gating technique using ionic liquids which allows to increase the capability of usual field effect doping by two order of magnitude opens a new avenue not only to novel physics of solid-state materials but also to potential applications for dissipationless devices. Here we report high-performance organic field-effect transistors with ionic-liquids electrolytes. With high carrier mobility of 12.6 cm²/Vs in the rubrene crystal that is order of magnitude larger than amorphous silicon devices, pronounced current amplification is achieved at the gate voltage of only 0.2 V, which is two orders of magnitude smaller than that necessary for organic thin-film transistors with dielectric gate insulators. The results demonstrate that the ionic-liquid/organic semiconductor interfaces are suited to realize low-power and fast-switching field-effect transistors without sacrificing carrier mobility in forming the solid/liquid interfaces.