An object is to provide a
semiconductor device with a novel structure. A
semiconductor device includes a first
transistor, which includes a channel formation region provided in a substrate including a
semiconductor material,
impurity regions, a first gate insulating layer, a first gate
electrode, and a first source
electrode and a first drain
electrode, and a second
transistor, which includes an
oxide semiconductor layer over the substrate including the semiconductor material, a
second source electrode and a second drain electrode, a second gate insulating layer, and a second gate electrode. The
second source electrode and the second drain electrode include an
oxide region formed by oxidizing a side surface thereof, and at least one of the first gate electrode, the first source electrode, and the first drain electrode is electrically connected to at least one of the second gate electrode, the
second source electrode, and the second drain electrode.