Previous studies of the reactions of silicon and germanium with molecular chlorine to form the volatile dihalide indicated that the slowest step in the surface reaction was the surface migration of a reaction intermediate. This paper reports the results of a similar investigation with molecular bromine. A molecular beam of bromine was modulated at frequencies below 100 Hz, and the volatile products of the reaction with heated single-crystalgermanium were detected mass spectrometrically using a lock-in amplifier with phase sensitive detection. The total reaction probability was determined as a function of surface temperature in order to ascertain the region of low surface coverage. Above about 800 °K the reaction probability was 0.3, nearly independent of surface temperature. In contrast to the reaction with chlorine both the tetra- and dibromides of germanium were formed. The phase detected GeBr 4 mass spectrometer signal lagged the GeBr 2 signal, indicating that GeBr 2 was a precursor for GeBr 4 formation. The time constants for their formation suggested that surface migration was the slow step in the surface reaction as in the case of GeCl 2 formation.