Using optical transmission and transmission electron microscopies, structural features of scanned laser crystallized amorphous Si films on Si3N4/glass substrates have been investigated as a function of the laser scan speed. We have found the existence of a critical speedVSC≃30 cm/sec below which only the solid‐phase furnace crystallization mechanism occurs yielding fine‐grained Si films. For laser scan speeds higher thanVSC, the crystallization mechanism is one of coherent and rapid crystallization, which has yielded Si films containing crystallites of dimensions up to 1×1 mm. For this regime, the velocity of the crystallization front is estimated to be as high as 1000 cm/sec.