Ga8Sb32S60 glass is modified by arsenic (As) to improve its thermal stability. Core/cladding fibers based on Dy3+-doped modified glass are fabricated. The optimized glass (Ga8Sb28As4S60) has excellent thermal and optical properties. Dy3+-doped Ga8Sb28As4S60 glass exhibits good mid-infrared emission properties. Fabricated fibers show a background loss of <2 dB/m in 2–6 μm spectral range.