Impurity levels in GaN HEMT devices make the design approaches of GaN-based PAs different from Si-based or GaAs-based PAs, and linearity is often achieved through system-level digital predistortion. The prevailing design approach is generally to prioritize one essential requirement, and then optimize other performance metrics. Reactive-matching PA (RMPA), distributed PA (DPA), feedback PA, push-pull PA and balanced PA design topologies are all explored. Load-modulated balanced amplifier (LMBA) design approaches are explored at length. Combining load-pull and real frequency techniques may prove to be an effective design approach. A number of example implementations and the achieved performance is presented to highlight the tradeoffs and limitations of the designs.