A simple and sensitive method has been devised for measuring the pressure dependence of the thermal conductivity of gases. The method uses the high thermoelectric power of a semiconductor for the accurate measurement of a temperature difference. Data at 25°C for argon, nitrogen, and helium to 3000 atm and carbon dioxide to 1300 atm are given. The results are compared with those of other investigators and agreement is generally better than 10%, using a two point calibration, and better than 3% using a multipoint calibration.