This paper describes the new technique of cooling electronic devices packaged in resin. In recent years, cooling electronic devices becomes very serious problem. To enhance thermal radiation from electronic devices, this problem is improved because 20%-40% of heat is dissipated by radiative heat transfer. We report new technique about cooling electronic devices to control radiative spectra from its surface. Resin which packages an electronic device prevents radiation from going outside air. We consider that radiation from electronic devices transmits resin to control radiative spectra. As a result, cooling performance improved. A spectral selective emitter which consists of periodical micron meter scale two-dimensional grating on metal surface can control radiative spectra. In this research, we decide an optimal selective emitter design from simulation and fabricated it by micro-machining technology. Finally, the fact that using spectral selective emitter enhanced cooling performance is obtained from cooling performance test.