An electrosurgical system has an electrosurgical generator with a multiple-phase RF output stage coupled to a multiple-electrode electrosurgical instrument. The instrument has three treatment electrodes each of which is coupled to a respective generator output driven from, for instance, a three-phase output transformer. Continuous RF output voltage waveforms are simultaneously delivered to respective generator outputs at the operating frequency, each waveform being phase-displaced with respect to the other waveforms. The magnitude of the RF output voltage waveform delivered to at least one of the generator outputs is sufficient to cause tissue vaporization at the respective treatment electrodes when the system is used for tissue treatment. Also disclosed is an electrosurgical generator in which the output transformer has windings forming at least three phases, the transformer core being constructed to provide at least three magnetic circuits each of which is inductively linked to the windings of at least two of the three phases.
