The present invention relates to a glass substrate for a high-frequency device, which includes SiO2 as a main component, the glass substrate having a total content of alkali metal oxides in the range of 0.001-5% in terms of mole percent on the basis of oxides, the alkali metal oxides having a molar ratio represented by Na2O/(Na2O+K2O) in the range of 0.01-0.99, and the glass substrate having a total content of Al2O3 and B2O3 in the range of 1-40% in terms of mole percent on the basis of oxides and having a molar ratio represented by Al2O3/(Al2O3+B2O3) in the range of 0-0.45, in which at least one main surface of the glass substrate has a surface roughness of 1.5 nm or less in terms of arithmetic average roughness Ra, and the glass substrate has a dielectric dissipation factor at 35 GHz of 0.007 or less.