The strong thermo-optic effect in silicon has been exploited for the fabrication of new sensing and communication devices. A temperature sensor, an electromagnetic energy sensor and an optical modulator are in particular presented. These devices, all working on interferometric principles, have been realized by means of the silicon standard microelectronic technologies, and are therefore suitable for full integration with on-chip circuitry. New thermo-optical materials are finally proposed with superior characteriztics, which still maintain the compatibility with VLSI technology.