An electrosurgical instrument that is capable of generating high-quality RF energy at a single frequency in the MHz range best suited for delicate, precise and quick-healing cutting procedures with low leakage currents using a monopolar handpiece, and also provides high-quality RF energy at the same frequency suited for use for carrying out similar procedures for use with a bipolar handpiece. In a preferred embodiment, the instrument is capable of generating sub-modes of electrosurgical currents with different waveforms optimized for cutting and hemostasis, and the various sub-modes are available for both the monopolar and bipolar handpieces. A preferred operating frequency is in the range of 4 MHz. The instrument includes means for maintaining a substantially constant power output irrespective of selection of one of the sub-modes.