A semiconductor device having favorable electric characteristics is provided. An oxide semiconductor layer includes first and second regions apart from each other, a third region which is between the first and second regions and overlaps with a gate electrode layer with a gate insulating film provided therebetween, a fourth region between the first and third regions, and a fifth region between the second and third regions. A source electrode layer includes first and second conductive layers. A drain electrode layer includes third and fourth conductive layers. The first conductive layer is formed only over the first region. The second conductive layer is in contact with an insulating layer, the first conductive layer, and the first region. The third conductive layer is formed only over the second region. The fourth conductive layer is in contact with the insulating layer, the third conductive layer, and the second region.