In this paper, the design and fabrication of a miniaturized class-F 2.5GHz 8W power amplifier using a commercially available GaN HEMT bare chip from TriQuint and a Selectively Anodized Aluminum Oxide (SAAO) substrate are presented. The SAAO process was recently proposed and patented by Wavenics Inc., Daejeon, Korea, which provides the fabrication of small size circuit comparable to conventional MMIC and at drastically low cost due to the use of aluminum as a wafer. The advantage of low cost is especially promising for RF components fabrication in commercial applications like mobile communications. The fabricated power amplifier has a compact size of 4.4 × 4.4mm² and shows power added efficiency (PAE) of about 35% and harmonic suppression of above 30dBc for second and third harmonics at an output power of 39dBm.