Thermal effect microsystems (TEMS) need a highly thermally insulated substrate. Porous silicon (PS) offers promising applications for insulation of thermal transducers from silicon wafers as its thermal conductivity is close to that of silicon oxide. A thorough investigation of PS thermal conductivity has been carried out regarding its technological parameters, i.e., porosity, thickness and oxidation temperature, by means of micro-Raman spectroscopy which yielded thermal conductivity values less than 2 W/m K as predicted by theoretical considerations. For TEMS, a 100-μm-thick meso-PS layer with a porosity of about 50% and oxidized at a moderate temperature (300 o C) presents the best attributes to ensure both an efficient thermal insulation, as its thermal conductivity value was found to be 0.6 W/m K, and a good mechanical strength.