Diffusion processes play a key role in the fabrication of semiconductor devices. For a long time the underlying mechanisms were thought to be analogous to those in metals, based on vacancies as thc dominant lattice defects in thermal equilibrium. From the mid‐sixties onwards it became clear that this picture is invalid for Si, where strongly relaxed self‐interstitials are dominant and responsible for self‐ and Group‐III‐ diffusion. Inter alia, this change of a paradigm led to novel concepts and to the quantitative explanation of the diffusion of so‐called hybrids such as Au, Pt, and Zn in Si by the so‐called kick‐out mechanism.