The parasitic thermovoltage can influence the temperature measurement during hyperthermia using the miniature multithermocouple probes with a common wire. It was noticed that, when a thermocouple junction is placed in a sharp thermal gradient, a parasitic thermovoltage is added to the voltage of all remaining thermocouples situated in the direction to the tip of the probe. This article gives the theoretical explanation, experimental verification, and practical elimination of this phenomenon.