A series of gallium-lanthanum-sulfide (GLS) glasses of different oxide concentration has been made and their spectroscopic properties, thermal properties, and the crystallization behavior of the glasses have been studied. It was revealed that the formability of GLS glasses relies on the existence of a certain amount of oxide content. The thermal stability of GLS glasses changes as a function of oxide concentration. The results have also shown that increasing oxide content caused a shift of the visible absorption edge to shorter wavelengths and an increase of absorption intensity in the infrared region at the multiphonon edge. Two closely related crystalline phases have been identified in the crystallized GLS glasses. For the first time it has been revealed that thermally stable GLS glasses can be made near the eutectic point of these two crystal phases by introducing an optimized amount of oxide.