The apparatus for on-die termination of a semiconductor memory includes a first ODT (On-Die Termination) voltage generating unit that outputs a first line voltage by calibrating an input voltage with a resistance ratio according to a first code having at least two bits; a first code calibrating unit that counts the first code according to the result of a comparison between the first line voltage and a reference voltage, stops the code count when the first code reaches a maximum value or a minimum value, and stores a code value based on a final count; a second ODT voltage generating unit that outputs a second line voltage by calibrating an input voltage with a resistance ratio according to the first code and a second code having at least two bits; and a second code calibrating unit that counts the second code according to the result of a comparison between the second line voltage and the reference voltage, stops the code count when the second code reaches the maximum value or the minimum value, and stores a code value based on a final count.