A theoretical approach to the problem of configuration fluctuation in Sm chalcogenides is presented. Properties of the fluctuating valence phase (also referred to as the collapsed phase) are discussed within an essentially localized model (ELM) in which most of the Sm 5delectrons are localized and only a small number (?0.1 electrons per Sm) occupy the free‐electron‐like states at the bottom of ad‐band. We argue that the ELM for the collapsed phase of SmS can account for almost all and, as far as we know, is inconsistent with none of the available experimental data.