A technical object of the present invention is to devise an alkali-free glass substrate having high devitrification resistance and high heat resistance. In order to achieve the above-mentioned technical object, the alkali-free glass substrate of the present invention includes as a glass composition, in terms of mol %, 60% to 80% of SiO2, 8% to 25% of Al2O3, 0% to less than 3% of B2O3, 0% to less than 1% of Li2O+Na2O+K2O, 0% to 10% of MgO, 1% to 15% of CaO, 0% to 12% of SrO, 0% to 12% of BaO, 0% to less than 0.05% of As2O3, and 0% to less than 0.05% of Sb2O3, and has a thickness of from 0.05 mm to 0.7 mm, a strain point of 700° C. or more, and a β-OH value of less than 0.20/mm.