We investigate the impact of firing treatment on n-type silicon wafers passivated by nand p-type polysilicon (polySi)/SiOx structure, and explore the root causes for the change of surface passivation quality upon firing. n-Type polySi passivated samples with SiNx capping layers show a slight increase of J0 after firing at 600 and 750, but exhibit a significant increase of J0, from 5 up to 40 fA/cm2 , when the peak firing temperature reaches 800. According to the hydrogen profiles measured in n-type polySi samples by secondary ion mass spectrometry (SIMS), there is a strong correlation between hydrogen concentration at the interfacial oxide and the peak firing temperature. Surprisingly, the surface passivation quality does not monotonically increase with the hydrogen content in the polySi layers. Additionally, it is found that the firing induced degradation in surface passivation can be recovered by the hydrogen out-diffusion process which was achieved through a thermal annealing. These results, in conjunction with the SIMS profiles indicate that an optimum hydrogen concentration in the polySi passivating contacts is essential for achieving an excellent surface passivation from polySi contact structures. In contrast to n-type polySi, p-type polySi passivated n-type wafers, are found to be stable upon firing, and the hydrogen content remains constant as the firing temperature varies from 700 to 900.