The known results of diffraction investigations of liquid, vitreous, and amorphous (film) semiconductors are examined with an aim at finding the general laws governing the structural changes in the crystal-melt, melt-glass, and crystal (vapor)-amorphous film transitions. These laws are formulated. A classification by structural attributes is proposed for liquid semiconductors. The role of the initial structure of the crystal in the formation of the structure of the short-range order of the melt is considered, the types of singularities of the structural changes accompanying melting in semiconductor-metal and semiconductor-semiconductor transitions are noted.