Semiconductor memory device capable of changing number of banks for refreshing when conducting refresh banks and Method of refresh thereof

In the method of generating an address specifying the memory bank that is a refresh target in the refresh operation of the semiconductor memory device, a bank address, as well as upon the refreshing operation of the semiconductor memory device by using a control address did not have a separate leverage during refresh operation refreshes the target is which it can be varied the number of memory banks. Therefore, it is possible to it is possible to change and further reducing the time allocated for the refreshment of the semiconductor memory device during the whole operating time of the system, improving the overall performance of the semiconductor system.