Gallium Nitride (GaN) MMIC processes suitable for operation at microwave frequencies are now commercially available from a number of vendors worldwide. The high breakdown voltage of GaN transistors and their ability to operate reliably at high junction temperatures make them well suited for the realization of high-power amplifiers. This case study describes the design and performance of a 25W X-band GaN PA MMIC developed with a 0.25µm GaN on SiC process.