The fundamental limitations of resistance-based thermometry and the desire to reduce sensor ownership have produced considerable interest in the development of photonics-based temperature sensors as an alternative to resistance thermometers. Photonic temperature sensors have the potential to leverage advances in frequency metrology to provide cost effective measurement solutions. We report on the fabrication and characterization of photonic-based nanoscale thermometers. Two types of temperature sensors, described in this work, a silicon photonic Bragg grating cavity and photonic crystal cavity devices, were fabricated using silicon-on-insulator CMOS-technology. The devices have built-in Fabry-Perot cavities, resonances wavelength of which shifts systematically with temperature. The sensitivity of photonic nanoscale thermometers can be tuned by a top-cladding material. When cladded with a poly(methyl methacrylate) thin layer, the sensitivity is 70 pm/degC, on the other hand, cladding with a silicon dioxide layer gives an improved sensitivity of 80 pm/degC. The described photonic thermometers have a temperature sensitivity that is at least seven to eight times better, compared to the sensitivity of conventional fiber Bragg grating sensors. We demonstrate that silicon photonic nanoscale thermometers are a viable temperature sensing solution.