An improved ac method to measure the thermal diffusivity in an extended temperature range is presented. The basic idea is to solder thermocouple wires directly on the sample, so that the sample itself acts as a thermocouple junction and the relaxation time for the temperature measurement becomes negligible. This new technique allows one to measure smaller samples and to increase the frequency of measurement so that the thermal losses could in principle be completely neglected. Finally, by the particular geometry a concurrent measurement of the electrical resistivity is obtained.