A semiconductor memory device controlling a program voltage according to the number of cells to be programmed and a method of programming the same. The semiconductor memory device includes a memory cell array. A write data buffer receives write data in a predetermined unit. A program cell counter calculates the amount of data, from the write data, to be programmed in the memory cell array. A program voltage generator outputs a program voltage to be applied to the memory cell array, in accordance with the amount of data to be programmed, at a time, in the memory cell array. The program voltage is controlled in accordance with the number of memory cells to be programmed.