A method for forming a semiconductor device is disclosed. In the semiconductor device, a gate is formed to enclose a fin structure in a 6F2 saddle fin gate structure transistor, so that the size of a channel region increases. In accordance with an aspect of the present invention, a method for forming a semiconductor device includes: defining an active region by forming a device isolation film over a semiconductor substrate; forming a first recess extending to a first level in the active region; forming a sacrificial film at a lower portion of the first recess; forming a fin structure over the sacrificial film; separating the fin structure from the semiconductor substrate in the active region by removing the sacrificial film and forming a hole between the fin structure and the active region; and forming a gate to enclose the fin structure.