Compared to metallic thin films or wires thick film resistors have a rather complex structure. Transition metal oxide particles are embedded into a glassy matrix. The resistivity depends heavily on the percentage of the constituents in the composition. It is believed that the main part of the resistance stems from the touching areas of conductive grains and that the conduction is by tunneling.To give a better insight a noise spectrum analysis has been developed. A DC current is passed through the sample to be measured. The output noise voltage is analyzed between 1.6 Hz and 25 kHz using a commercial third-octave analyser.Results are given of an experiment in which the glassy matrix of thick film resistors was etched away step by step and the noise was measured vs. the number of etching steps.