The stability of equilibrium of a thick, elastic, infinitely long slab composed of an incompressible Mooney-Rivlin material is studied. The slab is placed between two perfectly rigid plates and subjected initially to uniform heating, and subsequently to a large homogeneous compressive strain. On this original thermoelastic deformation, a small deformation field and a weak temperature field ate superposed. Application of the boundary conditions results in a system of linear algebraic equations whose solution is associated with nontrivial configurations of the slab. An explicit relation between the slenderness of the slab and the critical compressive strain is found. A numerical example displays the influence of heating on the stability of the slab.