AlInN/GaN unpassivated High Electron Mobility Transistor (HEMT) on Sapphire substrate has yielded a maximum drain current density close to 2 A/mm in steady state. Superior gate length downscaling than AlGaN/GaN devices has been observed owing to the possibility of the use of ultra thin barrier layer while keeping extremely high sheet carrier density. We reached an extrinsic current gain cut-off frequency of 70 GHz for a 0.08 mu m gate length device. Large signal measurements reveal a relatively low RF power dispersion. Indeed, at 10 GHz we performed for the first time power measurements on such a HEMT structure. We achieved 1.5 W/mm output power density at low bias condition (V-DS = 15V) in agreement with the expected power in spite of a strong thermal effect due to the sapphire substrate, a large leakage current in the Schottky diode characteristic and a low buffer layer resistivity. These results demonstrate the great potential of this structure for extremely high power high frequency applications.