Thermal treatment of poly-Si/SiO2/Si(100) structures at temperatures above 850 degreesC is found to generate Si(100)/SiO2 interface states related to P-b0 centers, which are not generated in the samples subjected to annealing without the poly-Si layer on. Generation of P-b0 centers indicates that during the anneal hydrogen is released from the poly-Si/oxide stack. This H release may be related to the growth of poly-Si grains and/or to the chemical interaction between the poly-Si and SiO2.