A 3D semiconductor device including: a first level, where the first level includes a first layer, the first layer including first transistors, and where the first level includes a second layer, the second layer including first interconnections; a second level overlaying the first level, where the second level includes a third layer which includes second transistors, and where the second level includes a fourth layer, the fourth layer including second interconnections; and a plurality of connection paths, where the plurality of connection paths provide first connections from a plurality of the first transistors to a plurality of the second transistors, where the second level is bonded to the first level, where the bonded includes oxide to oxide bond regions, where the bonded includes metal to metal bond regions, where the third layer includes crystalline silicon, and where the second level includes at least one scan-chain to support circuit test.