The continuous and rapidly growing demand for mobile communication access led to a major increase in the number of base stations worldwide to provide sufficient coverage and quality of service. As a consequence, mobile communication networks have become a significant contributor to global energy consumption. Several advanced topologies for efficiency improvement of RF power amplifiers have been developed. Modulating the amplifier's supply voltage according to the variation of the envelope signal is one of the most promising concepts. This topology is investigated here, with an architecture that switches the supply voltage of the power amplifier in discrete levels with a class-G supply modulator. The thesis addresses comprehensively all aspects of class-G supply modulation. Several prototype designs were realized to validate the theory and to gain experience on the influence of the corresponding parameters. These include the discrete supply voltage levels, the switching thresholds, and the interface between the RF PA and the class-G supply modulator. Efforts both on improving the RF power amplifiers and developing several class-G supply modulators were also involved. This work covers the progress up to a PA module that provides an instantaneous modulation bandwidth of 120 MHz and achieves better performance than state-of-the art continuous supply modulation systems. Class-G supply modulated RF power amplifiers based on gallium nitride technology exhibit a strong nonlinear behavior, therefore linearization is required. For this purpose, the linearization with digital predistortion based on behavioral models is optimized for the class-G topology and a novel predistorter model is developed and analyzed.