Silicon nitride nanocapacitors play an important role in micro- and nanoelectronic devices to be used under the action of ionizing radiation. Infrared spectrometry has been used to monitor the radiation stability of the products [1]. However, in addition to the effect of ionizing radiation, thermal effects must also be considered. The impact of thermal effects on the chemical bonds has recently been estimated for the thin films on the Si-containing surfaces. However, the estimation of the long-term stability of the substrate is still required. Therefore, in the present research, the stability of chemical bonds in Si substrates was analysed. The selected Si wafers, as satellite samples, were treated analogously to those used in the fabrication process of the thin films [3]. After preparation, the Si samples were heated to 150 °C at a rate of 10 °C/min, held at 150 °C for 8 hours, and allowed to cool to room temperature (one heating cycle). Fourier transform infrared (FTIR) spectra were measured after each of the heating cycles. Up to three FTIR measurements were performed for each sample. A total of 33 heating cycles were performed. The FTIR measurements were performed on a Bruker Vertex 70v spectrometer equipped with an attenuated total reflection module. In the FTIR spectra, the main signal occurs at 600–630 cm–1, corresponding to Si-Si asymmetric vibrations. The variations in the signal intensity are used to determine the thermal stability of the Si structures. The slope of the signal at 610 cm–1 shows to less than 0.1% changes over the 264 h cyclic heating tests, indicating the stability of the thin films. The obtained results will be used for further development of nanocapacitors with improved dielectric layers. [1] Romanova, M.; et al. Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms, 2020, 471, 17–23. [2] Avotina, L.; et al. Materials, 2023. 16, 17, 5781, 1–11. [3] Goldmane, A. E.; et al. Journal of Physics: Conference Series 2023, 2423 012022.