  The temperature behaviour of meson condensates $<\sigma_0>$ and $<\sigma_8>$
is calculated in the $SU(3)\times SU(3)$-linear sigma model. The couplings of
the Lagrangian are fitted to the physical $\pi,K,\eta,\eta'$ masses, the pion
decay constant and a $O^+(I=0)$ scalar mass of $m_\sigma=1.5$ 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 $<\bar q q>$ and strange $<\bar s
s>$-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 $T_c\sim 161$ MeV. At this temperature the
spontaneously broken subgroup $SU(2)\times SU(2)$ 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 $T\geq T_c$.
