Chalcogenide glasses with compositions Ge7.5AsyTe92.5−y (y=20, 40, 45, 47.5, 50, 52.5, 55) and Ge10AsyTe90−y (y=15, 20, 22.5, 35, 40, 45, 50) have been prepared by the melt-quenching technique. The amorphous nature of these glasses has been confirmed by X-ray powder diffractometry. The thermal stability of these glasses has been studied using differential scanning calorimetry (DSC). The compositional dependence of the glass transition temperature,Tg, the crystallization temperatures,Tc1 andTc2, and the melting temperature,Tm, are reported. The glass-forming tendency,Kgl, and the activation energy of crystallization,E, are calculated. The activation energy decreases with increasing tellurium content for both sets of glasses.