The mechanism of formation of the kink in the impurity profile of phosphorus‐diffused layers in silicon is shown to be related to the ``tail'' that is formed during low‐temperature heat treatments. The concentration at which the tail is formed is a function of temperature with an activation energy of 0.79 eV. The enhanced diffusion which gives rise to the tail depends on processes occurring in the high‐concentration region. A complex model is required to explain all of these results.