Provided is a glass plate for a substrate, which comprises, as a glass matrix composition as represented by mass % based on oxide: SiO2: 70 to 80, Al2O3: 0.1 to 5, B2O3: 0 to 3, MgO: 9.5 to 12, where the amount of CaO+SrO+BaO is 0 to 2, and the amount of Na2O+K2O is 12.5 to 15.5, which has a density of at most 2.5 g/cm3, has an average coefficient of thermal expansion from 50 to 350° C. of more than 75×10−7/° C. and at most 87×10−7/° C., has a glass transition point of at least 560° C., has a brittleness of at most 6.5 μm−1/2, and has a heat shrinkage (C)of at most 20 ppm.