A semiconductor device or a memory device with a reduced area, a large storage capacity, a high-speed operation, or low power consumption is provided. The semiconductor device includes a first transistor, a second transistor, a capacitor, a first wiring, a second wiring, a sense amplifier circuit, a decoder, a step-up circuit, a level shifter, and a buffer circuit. The first wiring is electrically connected to the buffer circuit and a second gate electrode of the first transistor. The second wiring is electrically connected to the sense amplifier circuit and the drain electrode of the second transistor. The capacitor is electrically connected to the drain electrode of the first transistor and the source electrode of the second transistor.