Different surface passivation approaches are applied on Cz-Si and FZ-Si samples and long-term stability is investigated during treatments at 60-80 degrees C and up to 1 sun equivalent illumination intensity. It is shown that SiNx:H and AlOx :H/SiNx:H surface passivation show a much more stable passivation quality when deposited on P-diffused and B-diffused surfaces, respectively. Long-term measurements lead to the conclusion that Cz-Si samples fired at measured peak temperatures up to 750 degrees C are very stable after regeneration of bulk defects. Samples fired at 850 degrees C show much stronger bulk-related degradation potentially linked to light and elevated temperature induced degradation (LeTID). Furthermore, Cz-Si samples fired at 850 degrees C express an instable behavior after a regeneration treatment.