Abstract: A memory module on a printed circuit board (PCB) has double density without increasing the area and height thereof. The memory module includes a first memory bank and a second memory bank that share data lines on the PCB. Each bank includes a group of packaged semiconductor memory devices. The memory module of the invention additionally includes a programmable logic device (PLD). The PLD outputs signals that selectively enable one of the first and second banks, in response to a bank select signal and control signals received from a memory controller. The package of the plurality of semiconductor memory devices is a shrink Thin Small Outline Package (sTSOP) or a chip size package (CSP) or plastic in which a length and a width are similar to each other.