Heat transfer from small heating elements on a substrate was studied experimentally and analytically. In one of the experiments, the heating elements are diodes, each having the size 20μm×20μm, and the substrate is a real IC chip. In another set of experiments, the heaters are narrow strips of In2O3, each being 20μm×20μm, deposited on a glass plate. In both sets of the experiments the heaters are activated singly or simultaneously, and cooled by forced convection of air, in either impinging jet or channel flow. The analytical interpretation of the experimental data indicates that heat conduction from the heat source to the substrate is an important factor in the determination of the maximum temperature at the source, while the surface heat transfer determines the bulk temperature of the substrate. The superposition of the temperature solutions is a vital method to estimate the temperature field in the presence of multiple heat sources in close proximity to each other.