We report the first time-resolved x-ray scattering study of the homoepitaxial growth of GaAs by organometallic vapor-phase epitaxy. The growth mode was determined to be layer-by-layer by observing 1-Hz oscillations of the x-ray intensity from the 11l crystal truncation rod near the 110 position. We show that the spatial distribution of islands can be dynamically determined by measuring the x-ray diffuse scattering near the 110. Finally, we show that significant correlations exist between the locations of islands during layer-by-layer growth. © 1992 The American Physical Society.