Traces of nine elements, gold, arsenic, cobalt, chromium, copper, europium, hafnium, sodium and antimony in commercially available silicon crystals were determined by the instrumental neutron activation analysis using the single comparator method. The values of the concentrations of these elements in both single and polycrystals were found to decrease significantly to a low limiting level by simply washing and etching surface contaminants having been introduced during various steps of sample preparation and irradiation. However, the chromium levels in polycrystals were not easily decreased, these depending upon the cutting tools employed. The Sb-doped content in each semiconductor has been compared with the associated quantities such as the concentration and the conductivity range given by the sample donor. Uncertainty in the sodium analysis due to the fission neutron reaction by silicon itself was discussed.