SEMICONDUCTOR DEVICE

A semiconductor device includes a first conductive layer, a first insulating layer on the first conductive layer, an oxide semiconductor layer on the first insulating layer, and second and third conductive layers on the oxide semiconductive layer. The oxide semiconductor layer includes a first region, a second region in contact with the second conductive layer, a third region in contact with the third conductive layer, a first impurity region between the first region and the second region, and a second impurity region between the first region and the third region. The first impurity region is in contact with the second conductive layer. The second impurity region is in contact with the third conductive layer. An electrical conductivity of each of the first impurity region and the second impurity region is greater than an electrical conductivity of each of the second region and the third region.