This paper investigates the long‐term stability of three different types of thermistor with room‐temperature resistances ranging from 80 to 150 k&OHgr;. Precision measurements of thermistor resistance and temperature were made in a thermal environment controlled to ±3 &mgr;K. Measurements took place in between periods of limited thermal cycling and also during 100 days at constant temperature. Mechanical shock and strain appear to be the cause of the high drift rates observed in some thermistors; the majority of the thermistors were, however, very stable, with drift rates around 0.1 mK per 100 days and were unaffected by thermal cycling. Such low drift rates indicate that certain thermistors could be used as convenient temperature transfer standards with a reproducibility in the submillikelvin range.