The heat transport from a chip due to conduction and interphase haet transfer from the chip to the surrounding air is investigated. Experiments are performed with thin diaphragms of silicon nitride, which can be heated by a thin-film resistor. The heat losses of the devices are measured is vaccum and in air. The influence of temperature, geometry, and heat sinks in investigated. Heat transfer is described by the transfer coefficient, which is a function of the temperature and the size of the chip. The calculated heat losses are in good agreement with the experimental values.