Recently, integrated flexible devices based on silicon nanowires (Si-NWs) have received significant attention as high performance flexible devices. However, most previous assembly methods can generate only specifically-shaped devices and require unconventional facilities, which has been a major hurdle for industrial applications. Herein, we report a simple but very efficient method for assembling Si-NWs into virtually generally-shape patterns on flexible substrates using only conventional microfabrication facilities, allowing us to mass-produce highly flexible low-noise devices. As proof of this method, we demonstrated the fabrication of highly bendable top-gate transistors based on Si-NWs. These devices showed typical n-type semiconductor behaviors, and exhibited a much lower noise level compared to previous flexible devices based on organic conductors or other nanowires. In addition, the gating behaviors and low-noise characteristics of our devices were maintained, even under highly bent conditions.