A thin film semiconductor device has a semiconductor thin film with a film
thickness of 200 nm or less. The semiconductor thin film is formed over a
dielectric substrate with a warping point of 600.degree. C. or lower. The
semiconductor thin film has a region in which a first semiconductor thin
film region with the defect density of 1.times.10.sup.17 cm.sup.-3 or
less and a second semiconductor thin film region with the defect density
of 1.times.10.sup.17 cm.sup.-3 or more are disposed alternately in the
form of stripes. The width of the first semiconductor thin film region is
larger than the width of the semiconductor thin film region. The grain
boundaries, grain size and orientation of crystals over the dielectric
substrate are controlled, so that a high quality thin film semiconductor
device is obtained.