Abstract: In a high frequency plasma power supply comprising a final stage push-pull amplifier 2 with each phase having a parallel combination of at least two FETs, an output transformer 5 having the connection of the phase outputs of the push-pull amplifier 2 to the opposite terminals of a primary winding with a neutral tap, and a low pass filler 6 allowing passage of substantially the fundamental frequency component from the secondary winding output of the output transformer 5, the high frequency power passing through the low pass filter being supplied between the electrodes of a plasma chamber 10 through an impedance matching circuit 9 having an impedance adjusting mechanism,the dc voltage Vds to be applied between the drain and source of each FET of each phase of the push-pull amplifier is adjusted to not more than about 30% of the dc absolute rated value and the turn ratio of the output transformer is 1:4, thereby supplying the power having the level necessary for plasma reaction.