Sigma 9 grain boundaries (Sigma 9 GBs) in the multicrystalline silicon substrates with and without annealing process were characterized by micro X-ray fluorescence, transmission electron microscopy (TEM) observation, and UV-Raman spectroscopy mapping. The Ni aggregations appeared at some Sigma 9 GBs only after annealing. The differences in the characteristics of GBs with and without annealing were evaluated. Clear structure changes were observed by TEM evaluation for the corresponding Sigma 9 GBs after annealing. At the same Sigma 9 GBs, the stress concentration was observed without an annealing process and disappeared with one. We consider that the Ni aggregation was enhanced by stress accumulation and silicide accelerated the atomic rearrangement at the Sigma 9 GBs. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3423445] All rights reserved.