X-ray photoelectron spectroscopy (XPS) was used to examine the MAPbI3/Si interface (MA = methylammonium) before and after 45 days of exposure to light, heat stress at 85 °C or 50% relative humidity (RH). From the survey XPS spectra it follows that under these external influences, changes in the I/Pb ratio, indicating the presence of the PbI2 phase as a degradation product, do not go beyond 12%. These results were confirmed by measurements of high-resolution XPS spectra in the energy ranges of Pb 4f, I 3d and valence band signals, which do not show significant high-energy shifts towards the energy position of the PbI2 reference spectra. © 2024.