A semiconductor device with less variation in transistor characteristics is provided. The semiconductor device includes a semiconductor film, a pair of blocking films over the semiconductor film, and an insulating film provided over the semiconductor film and between the pair of blocking films. The semiconductor film includes a pair of n-type regions and an i-type region provided between the pair of n-type regions. The n-type regions overlap with the blocking films. The i-type region overlaps with the insulating film.