A thin film transistor with favorable electric characteristics is provided. The thin film transistor includes a gate electrode, a gate insulating layer, a semiconductor layer which includes a microcrystalline semiconductor region and an amorphous semiconductor region, an impurity semiconductor layer, a wiring, a first oxide region provided between the microcrystalline semiconductor region and the wiring, and a second oxide region provided between the amorphous semiconductor region and the wiring, wherein a line tangent to the highest inclination of an oxygen profile in the first oxide region (m1) and a line tangent to the highest inclination of an oxygen profile in the second oxide region (m2) satisfy a relation of 1