Temperature is a fundamental parameter in the study of physical phenomena. At the nanoscale, local temperature differences can be harnessed to design novel thermal nanoelectronic devices or test quantum thermodynamical concepts. Determining temperature locally is hence of particular relevance. Here, we present a primary electron thermometer that allows probing the local temperature of a single electron reservoir in single-electron devices. The thermometer is based on cyclic electron tunneling between a system with discrete energy levels and a single electron reservoir. When driven at a finite rate, close to a charge degeneracy point, the system behaves like a variable capacitor whose magnitude and line-shape varies with temperature. In this experiment, we demonstrate this type of thermometer using a quantum dot in a CMOS nanowire transistor. We drive cyclic electron tunneling by embedding the device in a radio-frequency resonator which in turn allows us to read the thermometer dispersively. We find that the full width at half maximum of the resonator phase response depends linearly with temperature via well known physical law by using the ratio $k_text{B}/e$ between the Boltzmann constant and the electron charge. Overall, the thermometer shows potential for local probing of fast heat dynamics in nanoelectronic devices and for seamless integration with silicon-based quantum circuits.
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