We previously reported that crystalline silicon films for solar cells with high crystal uniformity (Si (100) texture) and very low defect density could be fabricated by zone melting crystallization (ZMC). The defects of the ZMC films were concentrated at the interface between the Si film and the top SiO2 film. The top SiO2 film was needed to fabricate smooth and uniform Si films. In this study, we attempted to fabricate smooth and uniform Si films without concentrating defects at the surface by using a new method of gas-flow zone melting crystallization (gas-flow ZMC). Instead of the top SiO2 film, the gas-flow ZMC used a flow of N-2 gas to the melting zone as a meams to prevent the formation of the rough surface. When the width of the melting zone was narrowed to 2.2-5.2 mm by the cooling effect of the gas flow, the gas-flow ZMC films had a smooth surface, uniform thickness and low defect density at the surface. However, the gas-flow ZMC films had several different crystal faces and the interior of the films had at least 60 times higher defect density than did that of the ZMC films. This result indicated that the top SiO2 film functioned to orient the (100) crystal face and that the crystal orientation of the (100) crystal face prevented the defect formation inside the ZMC films. If the stability of the interface between the Si film and the bottom SiO2 film can control the crystal orientation of the gas-flow ZMC films by thinning the Si film, the defect density of the gas-flow ZMC films is expected to be lower than that of the ZMC films.