Fiber Bragg gratings (FBG) were written through the polymer jacket of low-loss single mode As(2)S(3) chalcogenide fibers by using femtosecond laser pulses at 800 nm and a phase-mask. Peak reflectivity in excess of 99% was obtained at 3440 nm after 5 min of exposure. The resulting FBG maintained a peak reflectivity of 90% after 64 min of thermal annealing at 100 °C. This demonstration paves the way to the development of all-fiber mid-infrared laser sources.