Data storage devices are provided. A data storage device includes a memory transistor on a substrate and a data storage structure electrically connected to the memory transistor. The data storage structure includes a magnetic tunnel junction pattern and a top electrode on the magnetic tunnel junction pattern. The top electrode includes a first top electrode and a second top electrode on the first top electrode, and the first and second top electrodes include the same metal nitride. The first top electrode includes first crystal grains of the metal nitride, and the second top electrode includes second crystal grains of the metal nitride. In a section of the top electrode, the number of the first crystal grains per a unit length is greater than the number of the second crystal grains per the unit length.