This paper presents a 1.3 kW resonant power amplifier using a Gallium Nitride (GaN) device at 13.56 MHz for wireless power transfer (WPT). The power amplifier driving the power transmitting coils is based on a Class Φ2 inverter, a single switch topology with low switch voltage stress and fast transient response. This implementation utilizes a recently available GaN device in a low inductance package that is compatible with operation in the 10's of MHz switching frequency. These power GaN switching devices have low gate resistance RG and low capacitance CGS which greatly reduces the power requirements of the gate drive circuitry. This paper shows experimental measurements of the inverter in a WPT application and characterization of the system performance over various distances and operating conditions.