The present invention provides a glass substrate in which in a heat treatment step of sticking a silicon substrate and a glass substrate to each other, an alkali ion is hardly diffused into the silicon substrate, and a residual strain generated in the silicon substrate is small. A glass substrate of the present invention has: an average thermal expansion coefficient α50/100 at 50° C. to 100° C. of 2.70 ppm/° C. to 3.20 ppm/° C.; an average thermal expansion coefficient α200/300 at 200° C. to 300° C. of 3.45 ppm/° C. to 3.95 ppm/° C.; a value α200/300/α50/100 obtained by dividing the average thermal expansion coefficient α200/300 at 200° C. to 300° C. by the average thermal expansion coefficient α50/100 at 50° C. to 100° C. of 1.20 to 1.30; and a content of an alkali metal oxide being 0% to 0.1% as expressed in terms of a molar percentage based on oxides.