The practical utilization of all-solid-state sodium batteries necessitates the development of a mass synthesis process for high-alkali-content sulfide glass electrolytes, which are characterized by both high ionic conductivity and remarkable formability. Typically, vacuum sealing and quenching are conventional techniques employed during the manufacturing process. In this paper, we present a novel approach, a pioneering method for the production of sulfide glass electrolytes with high alkali concentrations, achieved through ambient-pressure heat treatment and a gradual cooling process. We enhance the glass-forming ability of Na3BS3 by incorporating a small quantity of SiO2. The ionic conductivity of the resulting Na3BS3·0.225SiO2 (molar ratio) glass exhibited 1.5 × 10-5 S cm-1 at 25 °C, surpassing that of Na3BS3 glass. An all-solid-state cell utilizing Na3BS3·0.225SiO2 glass is successfully operated as a secondary battery at 60 °C. Our findings suggest that sodium oxythioborosilicate glass with electrochemical properties identical to those of Na3BS3 can be prepared without the need for quenching. These results propel the advancement of research in the domain of mass production processes tailored for high-alkali-content sulfide glass.