  In the instanton models the chiral phase transition is driven by a transition
from random instanton-antiinstanton liquid and correlated
instanton-antiinstanton molecules. So far this phenomenon was studied by
numerical simulations, while we develop alternative semi-analytic approach. For
two massless quark flavors, both instantons and ``molecules" generate specific
4-fermion effective interactions. After those are derived, we determine the
temperature dependence of the thermodynamic quantities, the quark condensate
and the fraction of molecules using standard mean field method. Using
Bethe-Salpeter equation, we calculate T-dependence of mesonic correlation
functions.
