A transient one‐dimensional heat‐flow technique for absolute determination of thermal conductivity of solids has been developed. A commercial thermistor, pressed into contact with the front surface of a bar‐shaped test specimen typically 5–20 mm long, is used simultaneously as a constant heat source and as a sensor of the temperature increase. The measurement time is typically 5–10 s. Measurements on stainless‐steel and graphite standards from NIST indicate that the technique is accurate to within 3% in the thermal conductivity range 10–100 W m−1 K−1at room temperature.