Heat transfer from small heating elements on a substrate has been studied experimentally and analytically. In one of the experiments, the heating elements are diodes in an actual IC chip. In another set of experiments, heaters are small thin films deposited on a glass plate. In both experiments, the substrates are cooled by an impinging jet of air or channel flow. The experimental data indicate that heat conduction from the heating element to the substrate is an important factor in the determination of the maximum temperature of the element, while the surface heat transfer determines the bulk temperature of the chip. The numerical analysis clarifies that a chip surface with an area much larger than the element size is necessary for the heat transfer to the air flow.