Crystallization of amorphous silicon on oxide semiconductors using rapid-thermal annealing in vacuum is investigated. A 30nm n-type amorphous silicon (a-Si) is deposited on zinc-oxide (ZnO) and aluminum doped zinc-oxide (ZnO: Al) by PECVD on glass substrate. Rapid-thermal annealing for 30min to 180min of a-Si on ZnO and ZnO: Al were performed at 600°C. It is found that crystallization of a-Si on oxide semiconductors can be done in shorter time than that of standard solid-phase crystallization (SPC) of amorphous silicon on glass substrate at 600°C. It has been verified using Raman spectroscopy that a-Si on ZnO: Al changes into polycrystalline silicon (poly-Si) in 30min at 600°C.