  In the last few years, interest in monomolecular layers of transition metal
dichalcogenides (TMDs) has been driven by their unusual electronic and optical
properties, which are very attractive for designing functional elements of new
generation nanoelectronics. Recently, experimental evidence has appeared for
the formation of a high-temperature strongly bound electron-hole liquid (EHL)
in TMD monolayers. Strong binding of charge carriers is due to a significant
decrease in the screening of the Coulomb interaction in monolayer
heterostructures. In this work, the gas--liquid phase transition in a system of
electrons and holes in quasi-two-dimensional heterostructures based on TMDs is
considered and the critical parameters of such a transition are calculated. The
metal-insulator transition is described and the phase diagram for such
heterostructures is constructed.
