Today electronic power amplifiers are used in many scientific and industrial applications. For achieving high system efficiency, such systems are implemented almost exclusively as switch-mode power amplifiers (class-D amplifiers). By application of new semiconductor materials like gallium nitride (GaN) or silicon carbide (SiC) for the switching elements a further enhancement of efficiency and/or dynamic characteristic and bandwidth is possible. This thesis deals with the design and implementation of a switching amplifier with an actively damped LC output filter of higher order and 200 kHz switching frequency on the basis of GaN MOSFETs. Initially, the properties and advantages of these wide-bandgap transistors compared to conventional Si-MOSFETs are described. Subsequently, a concept for an actively damped LC output filter is reported and described. This section is followed by the generation of a mathematical model for the entire switching amplifier consisting of a PI-type output voltage controller, a switching-stage and a two-stage LC output filter with active damping by capacitor current feed-back. With this model, the switching amplifier is dimensioned in such a way that high bandwidth as well as good dynamic properties as, e.g., Butterworth or Bessel response are achieved. The filter and amplifier design is verified by numerical simulation using Matlab/Simulink and LTspice. For the practical implementation of the switching amplifier, a layout is developed minimizing the stray inductances of the power and driver circuit for the GaN MOSFETs. In addition, the design of the filter¿s LC components is performed and the circuit of the analog controller is designed. Finally, the measurement results of the test set-up are analyzed and compared to the numerical simulation, showing a good match of the results.