A unipolar nanodiode known as the self-switching diode has been demonstrated as a room-temperature terahertz detector, with its noise-equivalent-power value comparable to those of the state-of-the-art Schottky diodes. Here, we study its performance at elevated temperatures and show an unusual reduction in low-frequency noise, which may be useful for practical applications. The experiments suggest that the increased thermionic emissions result in the reduced device resistance and hence the lowered noise. The observed noise behavior appears to be in good agreement with Hooge’s mobility fluctuation theory.