We report on a novel, efficient, and one-step approach to prepare single-layer reduced graphene oxide (RGO) suspensions and films using hydroxylamine hydrochloride. The effective chemical reduction of GO was evidenced by a significant increase in the C/O ratio and five orders of magnitude decrease in the GO resistance. Field-effect transistor gas sensors were fabricated using as-produced RGO sheets and the resulting sensor exhibited a fast response and a high sensitivity to low-concentration target gases at room temperature.