We report on a systematic investigation of rapid thermal anneal (RTA) effects on the properties of FeMn exchange-biased magnetic tunnel junctions (MTJs). The tunneling magnetoresistance (TMR) in an as-grown MTJ is found to be ~27%, whereas the TMR in MTJs annealed by RTA increases with annealing temperature up to 300 o C, reaching ~46%. A significant change in the effective barrier thickness (t e f f ) and height (Φ e f f ) occurs within 10 s during RTA. Transmission electron microscopy and X-ray reflectivity studies demonstrate that the interface of the alumina tunnel barrier for the MTJ annealed by RTA became sharper and clearer, giving rise to the enhanced TMR.