This paper presents a 50 W floating-ground RF power amplifier for L-Band applications. The amplifier is intended to be used in a reverse-type envelope tracking system with supply voltages of up to 40 V. It accommodates signals with up to 80 MHz bandwidth for the supply modulation. The core element of the amplifier is a packaged floating-ground RF power GaN-HEMT, providing a wideband floating low-frequency ground and a good RF bypass to system ground in a well-defined environment. A saturated output power of 55 W at 1.3 GHz and power-added efficiencies from 57% to 47% in the 1.3 GHz to 1.6 GHz range make this amplifier an excellent candidate for highly efficient reverse-type envelope tracking systems with a performance comparable to conventional non-floating supply-modulated systems.