Abstract
Specimens of N‐type GaAs were found to become P‐type or less strongly N‐type as a result of heat treatment. The heat treatment was carried out in small quartz tubes, of two grades of purity. The magnitude of the changes was much less in high‐purity quartz. The effect in ordinary quartz was shown to be due in part to copper contamination, the copper originating in the quartz; the changes could be reduced by annealing.