Emerging GaN power switches show advantages for integration in power modules at high temperature and/or high efficiency. These modules are good candidates for embedded power converters in harsh environment such as three phase inverters for Electro-Mechanical Actuators (EMA) in the vicinity of internal combustion engines. The power range is usually within 1 to 5 kW, extending sometimes up to 50 kW, using a high voltage DC bus (HVDC) that is usually comprised between 200 V and 600 V. For aeronautical applications, GaN power switches could challenge SiC transistors for their high switching speed, hence reduced switching losses, therefore lower embarked mass. For automotive applications, it is the relative promise for lower cost per Amp that is pushing this technology up. This is why a project joining GaN device conception, power module development and gate driver optimization using high temperature technologies was setup. This paper presents the first practical results: a functional GaN power inverter-leg driven by a specific high temperature gate driver with signal and power insulation. This building block requires an auxiliary DC supply with a input voltage of 14 V or 28 V and an external PWM control signal. Current rating is 20 A and breakdown voltage is 200 V.