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In this article we investigate the spectral properties of the in…nitesimal generator of an in…nite system of master equations arising in the analysis of the approach to equilibrium in statistical mechanics. The system under consideration thus consists of in…nitely many …rst-order di¤erential equations governing the time evolution of probabilities susceptible of describing jumps between the eigenstates of a di¤erential operator with a discrete point spectrum. The transition rates between eigenstates are chosen in such a way that the so-called detailed balance conditions are satis…ed, so that for a large class of initial conditions the given system possesses a global solution which converges exponentially rapidly toward a time independent probability of Gibbs type. A particular feature and a challenge of the problem under consideration is that in the in…nite-dimensional functional space where the initial-value problem is well posed, the in…nitesimal generator is realized as a non normal and non dissipative compact operator, whose spectrum therefore does not exhibit a spectral gap around the zero eigenvalue.