The behavior of semiconductors is affected by the presence and distribution of dopants. The properties involved range from electrical resistivity and carrier concentration to gain boundary mobility and self-diffusion. Understanding these phenomena necessitates the characterization of defect structure and chemistry. STEM analysis has been applied to the measurement of arsenic segregation to silicon grain boundaries. Quantitative information on the boundary concentration of arsenic has been obtained both on as-deposited and annealed polysilicon specimens. In addition, the dynamic interaction of solutes with grain boundaries in polycrystalline germanium has been investigated. © 1984.