It is shown that the semiconductor-metal transition (SMT) in chalcogenide glass-forming liquids takes place over a range of temperatures and is accompanied by an endothermic effect and structural transformation. Therefore, it should be referred to as a smeared first-order phase transition with the micro-regions of co-operative structural transformations involving 10² or more atoms. Apparently, this mechanism of the SMT is determined by the structure of glass-forming liquids and glasses in which there are structurally self-consistent regions, i.e., by medium-range order.