A three-dimensional (3D) semiconductor structure with high density and method of fabricating the same are disclosed. The 3D semiconductor structure comprises at least a first memory cell and a second memory cell stacked on the first memory cell. The first memory cell comprises a first conductive line and a second conductive line. The second memory cell comprises another first conductive line opposite to the first conductive line of the first memory cell, and the second conductive line formed between said two first conductive lines of the first and second memory cells. The first and second memory cells share the second conductive line when the 3D semiconductor structure is programming and erasing, and each of the first and second memory cells has a diode.