The thermal gradients generated at submicrometer scale by the millions of transistors contained in integrated circuits are becoming the key limiting factor for device integration in micro- and nanoelectronics. Noncontact thermometric techniques with high-spatial resolution are, thus, essential for noninvasive off-chip characterization and heat management on Si surfaces. Here, the first ratiometric luminescent molecular thermometer implemented in a self-assembled polymer monolayer functionalized Si surface is reported. The functionalization of Si surfaces with luminescent thermometers constitutes a proof-of-concept that foretells a wide range of applications in Si-based micro- and nanostructures. The thermometric functionalization of the Si surface with Tb3+ and Eu3+ complexes leads to a thermal sensitivity up to 1.43% K-1, a cycle-recycle reliability of 98.6%, and a temperature uncertainty of less than 0.3 K. The functionalized surface presents reversible bistability that can be used as an optically active molecular demultiplexer.