The unusual magnetic and electrical properties of the semiconductor SmB6have been closely investigated recently. Primarily from magnetic susceptibility measurements, it has been hypothesized that the Sm valence changes from 3 + (4f5,6H5/2) at high temperatures to 2 + (4f6,7F0) at low temperatures. We have used the Mo¨ssbauer effect in149Sm to make a direct determination of the valence state by means of the ``isomer shift,'' which measures thes‐electron density at the Sm nucleus. This density changes with the 4fconfiguration because of coulombic shielding effects. Unfortunately, the change between 4f5and 4f6is too small to resolve resonance lines from the two charge states. The observed isomer shift of −0.4 mm/sec lies approximately halfway between the values (∼−0.9 and ∼0. mm/sec−1respectively) obtained for well characterized ionic di‐ and trivalent Sm compounds, and is not observed to vary between room temperature and 1.1°K. A new model is presented to explain both the magnetic susceptibility data and the Mo¨ssbauer results.