In this paper, we report a new process for molecular beam epitaxial (MBE) GaAs‐on‐Si growth. The process involves high‐temperatureinsituGaAs annealing above 850 °C. The unique points in this new approach are: (1) the thermal cycling layers or so‐called thermal strained superlattices (TSL) are inserted in buffer growth and found to be effective in blocking dislocation propagation; (2) a thin Al0.35Ga0.65As cap layer is deposited after GaAs buffer layer growth to prevent the underneath GaAs epitaxial layer from sublimation during annealing. An 850 °CinsituAlGaAs cap annealing (ACA) of the AlGaAs/GaAs buffer layer can eliminate all the twins and stacking faults in the buffer layers and yield high‐quality GaAs film. The bulk GaAs overlayers is grown at normal GaAs/Si growth temperature and is never exposed to a high anneal temperature. High‐quality GaAs/Si layers with surface dislocation densities 1×106cm−2and an x‐ray linewidth of 130 arc s have been achieved.