A semiconductor memory system is disclosed. In one embodiment, the semiconductor memory system and memory module of the present invention provides a buffer, wherein at least one write buffer chip on the memory module is only buffering and registering write data, command and address signals written from a memory controller to the memory chips. As read data are written back from each memory chip directly to the memory controller through unidirectional point-to-point read data lines the present semiconductor memory system achieves a low latency as compared with a fully buffered DIMM concept. As read data are only unidirectional a high transmission bandwidth can be achieved.