A memory device is provided. The memory device receives a main clock signal and provides an internal main clock signal; a data clock buffer to receive a data clock signal; and a latency control circuit configured to generate latency information based on the data clock signal and provide the latency information to a data circuit. The latency control circuit includes: a divider configured to generate divided-by-two clock signals based on the data clock signal; a divider configured to generate divided-by-four clock signals based on a first group of the divided-by-two clock signals; a first synchronization detector configured to output divided-by-two alignment signals indicating whether a second group of divided-by-two clock signals is synchronized with the data clock signal; and a latency selector configured to detect phases of the divided-by-four clock signals based on the divided-by-two alignment signals and adjust a latency of the main clock signal based on the phases.