To inhibit a metal element contained in a glass substrate from being diffused into a gate insulating film or an oxide semiconductor film. A semiconductor device includes a glass substrate, a base insulating film formed using metal oxide over the glass substrate, a gate electrode formed over the base insulating film, a gate insulating film formed over the gate electrode, an oxide semiconductor film which is formed over the gate insulating film and overlapping with the gate electrode, and a source electrode and a drain electrode which are electrically connected to the oxide semiconductor film. In a region of the base insulating film that is present in a range of 3 nm or less from a surface of the base insulating film, the concentration of a metal element contained in the glass substrate is less than or equal to 1×1018 atoms/cm3.