Application of a new thermal nano-probe based on the changes of electrical resistivity of a nanometer-sized filament with temperature has been presented for the thermal imaging of microwave power active devices. The filament is integrated into an atomic force scanning probe piezoresistive type cantilever. The novel thermal probe has a spatial resolution better than 80 nm and a thermal resolution of the order of 10-3 K. The measurements have been successfully performed on a 30 fingers GaAs-MESFET with a maximum power dissipation of 2.5 W. The microwave transistor has been implemented in a circuit in such a way to prevent the undesired microwave oscillations. In this case the power dissipation is equal to the dc power input. The near-field measurements have been compared with three-dimensional finite element simulations. A good agreement between simulations and measurements is achieved.

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