Resistivity changes caused by gold diffusion into silicon were studied in detail. The results did not agree with previous theoretical calculations. Radiotracer studies also showed that previously diffused n+ (phosphorus) layers greatly retard the diffusion of gold into silicon and increase its solubility. p + (boron) diffused layers do not retard gold diffusion but cause a more ideal type of diffusion. Autoradiographs showed lateral nonuniformity of gold concentration unless oxide formation is prevented during pretreatment, plating, and diffusion.