An object is to suppress conducting-mode failures of a transistor that uses an oxide semiconductor film and has a short channel length. A semiconductor device includes a gate electrode 304, a gate insulating film 306 formed over the gate electrode, an oxide semiconductor film 308 over the gate insulating film, and a source electrode 310a and a drain electrode 310b formed over the oxide semiconductor film. The channel length L of the oxide semiconductor film is more than or equal to 1 μm and less than or equal to 50 μm. The oxide semiconductor film has a peak at a rotation angle 2θ in the vicinity of 31° in X-ray diffraction measurement.