Stability properties of a thin liquid film subject to internal heat generation are studied within the framework of the long-wave theory. A strongly nonlinear evolution equation for the film interface is derived, studied, and solved numerically. Linear stability analysis is performed by a further reduction of the evolution equation. Internal heat generation is found to stabilize the film interface. The film is linearly stable if the intensity of internal heat generation is sufficiently strong. Within the range of linear instability the nonlinear evolution of the film results in the film rupture. ©1998 American Institute of Physics.