A novel semiconductor device or memory device is provided. Alternatively, a semiconductor device or memory device in which storage capacity per unit area is large is provided. The semiconductor device includes a sense amplifier provided to a semiconductor substrate and a memory cell provided over the sense amplifier. The sense amplifier includes a first transistor. The memory cell includes a capacitor over the semiconductor substrate, a second transistor provided over the capacitor, a conductor, and a groove portion. The capacitor includes a first electrode and a second electrode. The first electrode is formed along the groove portion. The second electrode has a region facing the first electrode in the groove portion. The second transistor includes an oxide semiconductor. One of a source and a drain of the second transistor is electrically connected to the second electrode through the conductor.