A method of forming a polycrystalline semiconductor film, which includes irradiating an amorphous semiconductor film formed on an insulating substrate with light to convert the amorphous semiconductor into a polycrystalline semiconductor with laterally grown crystal grains, thus forming a polycrystalline semiconductor film, wherein crystal growth in the semiconductor is controlled such that first crystal grains laterally grow in the first direction along a X-axis from the first group of initial nuclei, the second crystal grains laterally grow in the second direction opposite to the first direction along the X-axis from the second group of initial nuclei arranged apart from the first group of initial nuclei along the X-axis, and the first crystal grains collide against the second crystal grains at different points in time along a Y-axis.