The long‐term time‐dependent relaxation of the electrical resistance in several carbon and RuO2based temperature sensors at helium temperatures was investigated. The relative change of the resistance at fixed low temperature, measured immediately after sufficiently rapid cooldown has been found to be always logarithmic with time. In the helium temperature range, the spurious temperature drift associated with this effect for Allen–Bradley and Matsushita carbon radio resistors and for Philips RuO2based thick film sensors reaches about 1 mK per time decade, while for Rivac carbon film sensors it is an order of magnitude higher. The theoretical model explaining this relaxation based on the variable range hopping conductivity mechanism and the standard levels AHV theory of glasses at low temperatures was developed. ©1994 American Institute of Physics.