The growth of Si crystals from a Si-55.3 at%Al melts was investigated with the aim of developing a new Si refining process for SOG-Si production. Si crystals were grown by directional solidification of the Si-Al alloy. The temperature at the bottom of the sample was controlled from 1273 K (the alloy’s liquidus temperature) to 1173 K. Bulk Si crystals were successfully obtained in this study, and the crystal growth was found to be controlled by the diffusion of Si in the melt. By controlling the crystal growth conditions, the Al content of the Si crystals could be decreased to the level of the solid solubility of Al in Si; furthermore, other impurity elements could be efficiently removed by this refining method.