A memory system includes a semiconductor memory including memory cells and a memory controller configured to perform a first tracking process to determine a first voltage, and to read data using the first voltage in a read process after the first tracking process. In the first tracking process, the memory controller is configured to read only first, second, and third data respectively using a second, third, and fourth voltage, determine a number of first memory cells based on the first and second data, determine a number of second memory cells based on the second and third data, and determine the first voltage, based on the number of first and second memory cells.