SnSe is a semiconductor compound reported to possess very high thermoelectric ZT values at 600 °C to 700 °C. Oxidation and sublimation are of significant concern at such temperatures. The oxidation behavior of SnSe at four temperatures between 600 °C and 700 °C in atmospheric air was investigated by monitoring the weight change as a function of time as well as by characterizing the oxidized samples using optical microscopy, SEM with EDS, and powder XRD. The results show that SnSe oxidizes very rapidly at 600 °C to 700 °C to form SnO 2 and possibly Sn(SeO 3) 2. Sublimation of Se and Se oxides is also observed. At 600 °C the consumption of Sn from SnSe to form SnO 2 drives the composition to Se rich. A layer of SnSe 2 forms between the oxides and SnSe. At ≥ 650 °C the consumption of Sn likely leads to the formation of a transient liquid phase which significantly accelerates both oxidation and sublimation. It is concluded that SnSe needs to be used under vacuum or with a protective coating such as pure Si.