Provided are a method and apparatus for controlling a read latency of a high-speed DRAM. A memory device may include a delay measurement unit, a delay locked loop, a latency counter and a data output buffer. The delay measurement unit measures a delay time between when an external clock signal is input and when read data is output to generate measurement signals and generates a first internal clock signal delayed from the external clock signal. The delay locked loop (DLL) receives the first internal clock signal and generates a second internal clock signal synchronized with the external clock signal. The latency counter generates a latency signal from an external read command signal in response to the measurement signals, and the data output buffer outputs the read data in response to the latency signal and the second internal clock signal.