Characteristics of capillary-driven flow and phase-change heat transfer in a porous structure heated with a permeable heating source at the top were studied experimentally and theoretically in this paper. The experiments show that for small and moderate heat fluxes, the whole porous structure was fully saturated with liquid except adjacent to the horizontal heated surface where evaporation took place uniformly. For higher heat fluxes, a two-phase zone developed in the upper portion of the porous structure while the lower portion of the porous structure was saturated with subcooled liquid. When the imposed heat flux was further increased, a vapor blanket formed below the heated surface and the corresponding critical heat flux was reached. The heat transfer coefficient was modeled by simultaneously solving the problem of evaporating capillary meniscus in the pore level and the problem of fluid flow through a porous medium. The model is in good agreement with the experimental data, predicting the variations of the heat transfer coefficient with the increasing heating load.