A semiconductor device, including: a first layer including monocrystalline material and first transistors, the first transistors overlaid by a first isolation layer; a second layer including second transistors and overlaying the first isolation layer, the second transistors including a monocrystalline material; where the second layer includes at least one through layer via to provide connection between at least one of the second transistors and at least one of the first transistors, where the at least one through layer via has a diameter of less than 200 nm; a first set of external connections underlying the first layer to connect the device to external devices; and a second set of external connections overlying the second layer to connect the device to external devices.