  In the framework of deformation quantization we define formal KMS states on
the deformed algebra of power series of functions with compact support in phase
space as C[[\lambda]]-linear functionals obeying a formal variant of the usual
KMS condition known in the theory of C^*-algebras. We show that for each
temperature KMS states always exist and are up to a normalization equal to the
trace of the argument multiplied by a formal analogue of the usual Boltzmann
factor, a certain formal star exponential.
