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An object is to provide a semiconductor device with a novel structure in which stored data can be held even when power is not supplied and there is no limit on the number of write operations. The semiconductor device includes a first memory cell including a first transistor and a second transistor,

An object is to provide a semiconductor device with a novel structure in which stored data can be held even when power is not supplied and there is no limit on the number of write operations. The semiconductor device includes a first memory cell including a first transistor and a second transistor, a second memory cell including a third transistor and a fourth transistor, and a driver circuit. The first transistor and the second transistor overlap at least partly with each other. The third transistor and the fourth transistor overlap at least partly with each other. The second memory cell is provided over the first memory cell. The first transistor includes a first semiconductor material. The second transistor, the third transistor, and the fourth transistor include a second semiconductor material.

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1. A semiconductor device comprising: a substrate;a first transistor over the substrate;a second transistor over the substrate, anda capacitor electrically connected to the first transistor and the second transistor,wherein the first transistor and the second transistor are at least partially overla

1. A semiconductor device comprising: a substrate;a first transistor over the substrate;a second transistor over the substrate, anda capacitor electrically connected to the first transistor and the second transistor,wherein the first transistor and the second transistor are at least partially overlapped with each other with an insulating layer interposed there between,wherein each of the first transistor and the second transistor comprises a channel formation region comprising an oxide semiconductor,wherein a gate of the first transistor is directly connected to one of a source or a drain of the second transistor,wherein the capacitor comprises a first electrode, a second electrode, and a first insulating layer provided between the first electrode and the second electrode, andwherein the one of the source or the drain of the second transistor is the first electrode of the capacitor. 2. The semiconductor device according to claim 1, wherein the oxide semiconductor comprises indium. 3. The semiconductor device according to claim 1, wherein one of a source or a drain of the first transistor is connected to the other one of the source or the drain of the second transistor. 4. The semiconductor device according to claim 1, wherein the oxide semiconductor contains hydrogen at a concentration lower than or equal to 5×1019 atoms/cm3. 5. The semiconductor device according to claim 1, wherein the oxide semiconductor contains carriers at a concentration lower than or equal to 1×1012/cm3. 6. The semiconductor device according to claim 1, wherein off-state current per micrometer of a channel width of the second transistor is lower than or equal to 100 zA at room temperature. 7. The semiconductor device according to claim 1, wherein a top surface of the gate of the first transistor is directly connected to a bottom surface of the one of the source or the drain of the second transistor. 8. A semiconductor device comprising: a driver circuit comprising a first transistor, the first transistor comprising a channel formation region which comprises single crystal silicon;a first insulating layer over the first transistor;a second transistor over the first insulating layer;a second insulating layer over the second transistor;a third transistor over the second insulating layer, anda capacitor electrically connected to the second transistor and the third transistor,wherein each of the second transistor and the third transistor comprises a channel formation region comprising an oxide semiconductor,wherein a gate of the second transistor is directly connected to one of a source or a drain of the third transistor,wherein the second transistor and the third transistor are at least partially overlapped with each other,wherein the capacitor comprises a first electrode, a second electrode, and a first insulating layer provided between the first electrode and the second electrode, andwherein the one of the source or the drain of the third transistor is the first electrode of the capacitor. 9. The semiconductor device according to claim 8, wherein the oxide semiconductor comprises indium. 10. The semiconductor device according to claim 8, wherein one of a source or a drain of the second transistor is connected to the other one of the source or the drain of the third transistor. 11. The semiconductor device according to claim 8, wherein the driver circuit comprises a selector circuit. 12. The semiconductor device according to claim 8, wherein the channel formation region of the first transistor is formed in a single crystal silicon substrate. 13. The semiconductor device according to claim 8, wherein the oxide semiconductor contains hydrogen at a concentration lower than or equal to 5×1019 atoms/cm3. 14. The semiconductor device according to claim 8, wherein the oxide semiconductor contains carriers at a concentration lower than or equal to 1×1012/cm3. 15. The semiconductor device according to claim 8, wherein off-state current per micrometer of a channel width of the third transistor is lower than or equal to 100 zA at room temperature. 16. The semiconductor device according to claim 8, wherein a top surface of the gate of the second transistor is directly connected to a bottom surface of the one of the source or the drain of the third transistor. 17. A semiconductor device comprising: a substrate provided with a driver circuit, the substrate comprising single crystal silicon;a first insulating layer over the substrate;a first transistor over the first insulating layer;a second insulating layer over the first transistor;a second transistor over the second insulating layer; anda capacitor electrically connected to the first transistor and the second transistor,wherein each of the first transistor and the second transistor comprises a channel formation region comprising an oxide semiconductor,wherein a gate of the first transistor is directly connected to one of a source or a drain of the second transistor, andwherein the first transistor and the second transistor are at least partially overlapped with each other,wherein the capacitor comprises a first electrode, a second electrode, and a first insulating layer provided between the first electrode and the second electrode, andwherein the one of the source or the drain of the second transistor is the first electrode of the capacitor. 18. The semiconductor device according to claim 17, wherein the oxide semiconductor comprises indium. 19. The semiconductor device according to claim 17, wherein one of a source or a drain of the first transistor is connected to the other one of the source or the drain of the second transistor. 20. The semiconductor device according to claim 17, wherein the driver circuit comprises a selector circuit. 21. The semiconductor device according to claim 17, wherein the oxide semiconductor contains hydrogen at a concentration lower than or equal to 5×1019 atoms/cm3. 22. The semiconductor device according to claim 17, wherein the oxide semiconductor contains carriers at a concentration lower than or equal to 1×1012/cm3. 23. The semiconductor device according to claim 17, wherein off-state current per micrometer of a channel width of the second transistor is lower than or equal to 100 zA at room temperature. 24. The semiconductor device according to claim 17, wherein a top surface of the gate of the first transistor is directly connected to a bottom surface of the one of the source or the drain of the second transistor. 25. A semiconductor device comprising: a substrate comprising single crystal silicon;a first memory cell over the substrate, the first memory cell comprising a first transistor;an insulating layer over the substrate; anda second memory cell over the insulating layer, the second memory cell comprising a second transistor and a capacitor,wherein each of the first transistor and the second transistor comprises a channel formation region comprising an oxide semiconductor,wherein the first transistor and the second transistor are at least partially overlapped with each other,wherein the capacitor comprises a first electrode, a second electrode, and a first insulating layer provided between the first electrode and the second electrode, andwherein one of a source or a drain of the second transistor is the first electrode of the capacitor. 26. The semiconductor device according to claim 25, wherein a driver circuit comprising a transistor is provided between the substrate and the first memory cell, andwherein a channel formation region of the transistor is formed in the substrate. 27. The semiconductor device according to claim 25, wherein the oxide semiconductor comprises indium. 28. The semiconductor device according to claim 25, wherein the oxide semiconductor contains hydrogen at a concentration lower than or equal to 5×1019 atoms/cm3. 29. The semiconductor device according to claim 25, wherein the oxide semiconductor contains carriers at a concentration lower than or equal to 1×1012/cm3. 30. The semiconductor device according to claim 25, wherein off-state current per micrometer of a channel width of the second transistor is lower than or equal to 100 zA at room temperature. 31. A semiconductor device comprising: a first transistor comprising a first oxide semiconductor layer;a second transistor comprising a second oxide semiconductor layer; anda capacitor electrically connected to the first transistor and the second transistor,wherein an insulating layer is located between the first oxide semiconductor layer and the second oxide semiconductor layer,wherein a gate of the first transistor is directly connected to a source or a drain of the second transistor,wherein the capacitor comprises a first electrode, a second electrode, and a first insulating layer provided between the first electrode and the second electrode, andwherein the source or the drain of the second transistor is the first electrode of the capacitor. 32. The semiconductor device according to claim 31, wherein the second oxide semiconductor layer is located above the insulating layer. 33. The semiconductor device according to claim 31, wherein the insulating layer is a gate insulating layer of the first transistor. 34. The semiconductor device according to claim 31, wherein one of a source or a drain of the first transistor is connected to the other one of the source or the drain of the second transistor. 35. The semiconductor device according to claim 31, wherein the first oxide semiconductor layer comprises indium. 36. The semiconductor device according to claim 31, wherein the first oxide semiconductor layer contains hydrogen at a concentration lower than or equal to 5×1019 atoms/cm3. 37. The semiconductor device according to claim 31, wherein the first oxide semiconductor layer contains carriers at a concentration lower than or equal to 1×1012/cm3. 38. The semiconductor device according to claim 31, wherein off-state current per micrometer of a channel width of the second transistor is lower than or equal to 100 zA at room temperature. 39. The semiconductor device according to claim 31, wherein a top surface of the gate of the first transistor is directly connected to a bottom surface of the source or the drain of the second transistor.