Femtosecond filamentation of 800 nm laser pulses in the conditions of strong two-photon absorption was first directly observed in As ₄Ge₃₀S₆₆ chalcogenide glass. In this paper we also present the experimental results on laser self-written waveguides in arsenic-germanium-sulfide glasses. In contrast, there was no filamentation and spectrum widening in stoichiometric As₂S₃ glass. It was shown that nonlinear figure of merit was as high as 0.52 and only 0.04 in glassy As₄Ge₃₀S₆₆ and As₂S₃, respectively.