Abstract: Process for determining the donor content of polycrystalline silicon of high purity to be used in the semiconductor industries, the silicon having a known acceptor content of up to 0.02 atomic % and a donor content of up to 0.1 atomic %, the determination comprising the steps of introducing a test rod into a gas-tight quartz tube of only slightly larger internal diameter than the test rod, converting the rod into the oligocrystalline state by zone drawing with a seed crystal within a streaming protective gas, forming a melting zone in the test rod travelling vertically over the entire length, measuring the resistance of the so formed oligocrystalline test rod, and calculating the donor concentration from the measured resistance, the protective gas being a noble gas with an admixture of 10 - 800 ppm of oxygen.