This paper describes the design and measured performance of a 1-8GHz power amplifier MMIC fabricated with a 0.15um Gallium Nitride (GaN) process technology. The process features a 100um thick Silicon Carbide (SiC) substrate and compact transistor layouts with individual source grounding vias (ISV). The design utilizes a non-uniform distributed power amplifier (NDPA) topology with a novel trifilar connected output transformer. The 2-stage amplifier demonstrates 9.3-13.1W of output power over a 1-8GHz bandwidth with greater than 29% associated power added efficiency (PAE).