A simple test is developed to establish the existence of an Ohmic thermally activated conductivity in a chalcogenide glass which is carrying uniform current densities sufficient to cause current‐controlled negative differential resistance. The technique involves proper plotting of the turnover voltage data, taken as a function of ambient temperature, according to a theoretical relation obtained for a Joule‐heated thin‐film sandwich structure. This technique is of particular value in the event that insufficient information is available for a detailed analysis of the current‐voltage curve. Experimental data from a thin‐filma‐As2SeTe2device are plotted according to this relation and evidence is presented that the chosen conductivity function does not obtain for this glass at high current densities, even though this behavior is observed at low current densities.