Abstract The Parker Solar Probe (PSP) Fields Experiment (FIELDS) uses Radio Frequency Spectrometer (RFS) data and Quasi‐Thermal Noise Spectroscopy (QTN) to determine the temperature and density of electrons in the heliosphere. The FIELDS antennas typically operate with a negative bias current. We quantify the effect of the bias current on the shot noise spectrum by comparing spectra with a nominal negative bias current and spectra with minimal bias. The observed increase in the shot noise spectrum is smaller than the value determined by calculating currents based on measured instrument and plasma parameters. We discuss possible reasons for this discrepancy, and describe how quantifying the effects of the applied bias current on the shot noise spectrum can enable more accurate QTN spectroscopy.