To provide a glass substrate which has a high
glass transition temperature, which has a
thermal expansion coefficient close to that of
soda lime glass, which has a low
specific gravity, which will hardly undergo yellowing, and which further has good melting characters and is thereby produced with
high productivity.A glass substrate which has a composition comprising, as represented by
mass percentage based on oxides,SiO2 55 to 65%, Al2 O3 4 to 8%, MgO 6 to 9%, CaO 0.1 to 5%, SrO 0.5 to 6%, BaO 0 to 2%, MgO + CaO + SrO + BaO 6.6 to 19%, Na2 O 0 to 5%, K2 O 9.5 to 21%, Na2 O + K2 O 10 to 22%, ZrO2 0.5 to 5%, Fe2 O30.06 to 0.15%,which has a
specific gravity of at most 2.7, which has an average
thermal expansion coefficient from 50 to 350° C. of from 80×10−7 / ° C. to 90×107 / ° C., which has a
glass transition temperature of at least 640° C., and wherein when the
viscosity is η, the temperature at which log η=2 is satisfied is at most 1,550° C., and the yellow coloring b* on the glass surface is at most 8.