High temperature seal glass has stringent requirement on glass thermal stability, which is dictated by glass network structures. In this study, a SrO- La2 O3 - Al2 O3 - B2 O3 - SiO2 based glass system was studied using nuclear magnetic resonance, Raman spectroscopy, and x-ray diffraction for solid oxide cell application purpose. Glass structural unit neighboring environment and local ordering were evaluated. Glass network connectivity as well as silicon and boron glass former coordination were calculated for different B2 O3: SiO2 ratios. Thermal stability of the borosilicate glasses was studied after thermal treatment at 850 °C. The study shows that high B2 O3 content induces BO4 and SiO4 structural unit ordering, increases glass localized inhomogeneity, decreases glass network connectivity, and causes devitrification. Glass modifiers interact with either silicon- or boron-containing structural units and form different devitrified phases at different B2 O3: SiO2 ratios. B2 O3 -free glass shows the best thermal stability among the studied compositions, remaining stable after thermal treatment for 200 h at 850 °C. © 2008 American Institute of Physics.