As the transfer between a processor LSI and a memory has been increasing year by year, there is a demand for increasing the traffic amount and reducing the power required for communication. With this being the condition, a method of stacking LSIs thereby reducing the communication distance is being contemplated. However, the inventors have found that the reduction of cost in the stacking process and the increase in the degree of freedom of selecting the memory LSI to be stacked are required for a simple stacking of processor LSIs and memory LSIs as so far practiced. An external communication LSI including a circuit for performing the communication with the outside of the stacked LSI at a high rate of more than 1 GHz; a processor LSI including a general purpose CPU etc.; and a memory LSI including a DRAM etc. are stacked in this order and those LSIs are connected with one another with a through silicon via to enable a high speed and high volume communication at a shortest path. Further, an interposer for facilitating the connection with the processor LSI is connected to the input terminal of the memory LSI to be stacked thereby increasing the degree of freedom in selecting memories.