According to an embodiment, a power amplifier is provided with at least one first growth ring gate structure and multiple second growth ring gate structures. The first growth ring gate structure is bounded by a semiconductor layer and performs a power amplification operation. The multiple second growth ring gate structures are bounded by the semiconductor layer and are arranged adjacently around the first growth ring gate structure in a surrounding manner. When the first growth ring gate structure performs a power amplification operation, the multiple second growth ring gate structures are depleted by applying a reverse bias to the multiple second growth ring gate structures whereby the depleted multiple second growth ring gate structures isolate the first growth ring gate structure from a surrounding portion.