The temperature behaviour of meson condensates and
is calculated in the SU(3)×SU(3)-linear sigma model. The couplings of
the Lagrangian are fitted to the physical π,K,η,η′ masses, the pion
decay constant and a O+(I=0) scalar mass of mσ​=1.5 GeV. The quartic
terms of the mesonic interaction are converted to a quadratic term with the
help of a Hubbard-Stratonovich transformation. Effective mass terms are
generated this way, which are treated self-consistently to leading order of a
1/N-expansion. We calculate the light and strange <sˉs>-quark condensates using PCAC relations between the meson masses and
condensates. For a cut-off value of 1.5 GeV we find a first-order chiral
transition at a critical temperature Tc​∼161 MeV. At this temperature the
spontaneously broken subgroup SU(2)×SU(2) is restored. Entropy density,
energy density and pressure are calculated for temperatures up to and slightly
above the critical temperature. To our surprise we find some indications for a
reduced contribution from strange mesons for T≥Tc​.Comment: 17 pages, HD--TVP--93--15. (3 figures - available on request