A memory device includes a memory cell array that includes a plurality of memory cell rows, a temperature sensor that detects a temperature of the memory cell array and generates internal temperature data, a first register that stores external temperature data received from outside of the memory device, and a refresh control unit that determines a skip ratio of refresh commands received at a refresh frequency that corresponds to the external temperature data by comparing the internal temperature data and the external temperature data and performing a refresh operation for the plurality of memory cell rows in response to refresh commands skipped and transmitted based on the skip ratio.