We investigate the effect of a cosmological constant on the gravito-thermal instability. A spherically symmetric self-gravitating gas is studied as a thermodynamic system with long range interactions in the micro-canonical ensemble. The onset of the instability is calculated by the second order variation of the entropy and Poincare’s theory of series of equilibria. In the Newtonian limit of dS, the system presents a novel `reentrant behaviour’; in addition to the Antonov radius we find a second critical radius, where a series of local entropy maxima is restored. The relationship with Schwarzschild-dS system is investigated. The Tolman-Oppenheimer-Volkov equation with a cosmological constant is derived as a thermodynamic equilibrium equation by maximization of the entropy. For several equations of state the full general relativistic system is studied in the thermodynamic framework and the onset of instability is calculated.