•Stable and huge grain growth of Si thin films.•Orientations of {100} in the surface normal and scan directions.•Length of more than 3000 μm.•Width of 120-150 μm. A steady-state crystal growth of a {100}-oriented grain-boundary free 60 nm-thick Si thin-film is realized so long as the laser scan continues by the continuous-wave laser lateral crystallization of amorphous-Si on quartz, resulting in a huge grain of 3000 μm long and 120-150 μm wide. At an increased power by 0.1 W from the optimum power, a stable grain growth is realized as well, but it takes a longer scan travel to get the steady-state crystal growth than that at the optimum. With a disturbance on the way of the scan at the optimum power, the steady-state crystal growth continues to the vicinity of the disturbance, and it tends to recover with further scan after the disturbance even with the nano-crystal region formed at the disturbance region.