  We study thermodynamic properties of spatially separated electron-hole plasma
in double-layered systems using Green function formalism. The screening of the
Coulomb interaction is considered in the framework of Thomas-Fermi
approximation, and a qualitatively new mechanism of screening by indirect
excitons is taken into account. The exciton density is shown to decrease
sharply with increasing electron-hole separation up to one exciton Born radius.
The strong mutual enhancement of screening and charge-separation effects is
found.
