A semiconductor device includes a semiconductor layer including a channel region, and a first region and a second region to which an impurity element is introduced to make the first region and the second region a source and a drain, a third region, and a gate electrode provided to partly overlap with the semiconductor layer with a gate insulating film interposed therebetween In the semiconductor layer, the first region is electrically connected to the gate electrode through a first electrode to which an AC signal is input, the second region is electrically connected to a capacitor element through a second electrode, the third region overlaps with the gate electrode and contains an impurity element at lower concentrations than each of the first region and the second region.