The performance of GaAs SSPA's is crucial to a rapidly increasing number of systems. This tutorial aims at clarifying the design choices and trade-offs, and at warning the new designer for pitfalls and unexpected problems. The tutorial starts, after a brief introduction, with a survey of the relevant GaAs technologies. After this, the tutorial follows the steps of a normal broadband microwave GaAs SSPA design: The transistor unit cell and then the operating point are chosen and the trade-off between power and gain for the load impedance is made. The topology for the total amplifier is determined, based on paralleling sufficient transistors for the required output power, and adding stages to achieve the required gain. Finally the matching is performed, starting at the output and working its way back to the input. Everywhere, the stability of the transistors and the total amplifier is of concern. Oscillations pose the biggest threat to SSPA designers. Finally, the design steps are illustrated with a recent example of a 5-7 Watt, 30 dB gain HFET amplifier. At the end of the tutorial, a relatively long list of references is included. They were included especially to assist the new designer in finding his way in literature.