(AgSbTe2)(15)(GeTe)(85) (TAGS-85) is a p-type semiconductor characterized by a maximum dimensionless thermoelectric figure of merit of 1.4-1.7 at elevated temperature. In this study, the microstructure of as-solidified TAGS-85 at room temperature and elevated temperature (160 degrees C) was investigated using TEM. At room temperature, pervasive twinning was observed throughout the specimen. Upon heating to above 120 degrees C, some of the twins dissolved and new point defects began to nucleate. The mechanisms responsible for formation of high temperature defects are discussed.