An amorphous semiconductor film and a semiconductor film including an
element selected from Group 15 of the periodic table are formed over a
substrate. An island-shaped region including an island-shaped amorphous
semiconductor film and an island-shaped semiconductor film is formed. A
source electrode and a drain electrode are formed over the island-shaped
region. The island-shaped semiconductor film that is not covered by the
source electrode and the drain electrode is removed using the source
electrode and the drain electrode as a mask. At this time, the thickness
of the island-shaped amorphous semiconductor film is reduced, and a
portion of the island-shaped amorphous semiconductor film is exposed. A
catalytic element promoting crystallization is added into a region in
which the island-shaped amorphous semiconductor film is exposed. By a
heat treatment, the island-shaped amorphous semiconductor film is
crystallized and the catalytic element is gettered.