In a semiconductor element including an oxide semiconductor film as an active layer, stable electrical characteristics are achieved. A semiconductor element includes a base film which is an oxide film at least a surface of which has crystallinity; an oxide semiconductor film having crystallinity over the base film; a gate insulating film over the oxide semiconductor film; a gate electrode overlapping with at least the oxide semiconductor film, over the gate insulating film; and a source electrode and a drain electrode which are electrically connected to the oxide semiconductor film. The base film is a film containing indium and zinc. With the structure, a state of crystals in the oxide semiconductor film reflects that in the base film; thus, the oxide semiconductor film can have crystallinity in a large region in the thickness direction. Accordingly, the electrical characteristics of the semiconductor element including the film can be made stable.