As the basic component of photonic integrated circuits, optical reflectors are widely used in plenty of fields, such as quantum communications, smart grids, aerospace and so on. On-chip optical reflectors with high reflectance and low temperature sensitivity shall greatly simplify the photonic integrated circuit systems and improve the reliability and stability of the photonic integrated circuits. Therefore, we propose an on-chip optical reflector based on silicon on insulator with high reflectance and low temperature sensitivity. Our scheme is based on a Sagnac loop and can obtain ultra-high reflectance with a wavelength range of 3.41 nm (reflectance more than 90%) and high reflectance with a wavelength range of 32.85 nm (reflectance more than 80%). The reflectors are heated by the on-chip micro-electrodes, and the results show that when the power of the micro hot electrode is gradually increased from 0 mW to 6 mW, the wavelength shift of the reflector in the wavelength region of 1566.5-1568.58 nm is less than 0.045 nm. The reflectance change is less than 0.19 dB. The reflector has the advantages of small size, light weight, simple fabrication, high reflectance, low loss, and temperature insensitivity. It can be widely used in communication and signal processing fields such as lasers, microwave photonic filters, and optical transmission networks.