An analysis of a class D voltage-switching tuned power amplifier is given, along with experimental results. Analytical equations are derived for performance parameters at any operating frequency normalised with respect to the resonant frequency and at any load resistance normalised with respect to the characteristic impedance of the resonant circuit. The analysis is carried out under the high loaded quality factor assumption, using Fourier series techniques. The behaviour of power MOSFETs in class D circuits for both capacitive and inductive loads is discussed in detail. It is shown that the operation above the resonant frequency (an inductive load) is preferred. The theoretical results were in good agreement with measured circuit performance parameters. The equations provide easy-to-use design tools, which can find a broad application, e.g. in designing DC/DC resonant converters and DC/AC inverters.