A modular hybrid switching amplifier (HSA) for wide-bandwidth supply modulation of RF power amplifiers is presented. The HSA is designed for maximum 15 V supply voltage, 1 A supply current and 10 MHz bandwidth. The purpose is to compare alternative switch technologies. A case study is conducted on GaN-HEMT and Si-MOSFET, which are compared with regards to efficiency and linearity under different load conditions, based on simulations and on measurements of the fabricated designs. Design modifications to accommodate the alternative switch technologies are presented together with analysis of non-linearities including slew-rate induced amplitude distortion. © 2012 Institut f r Mikrowellen.