A semiconductor device includes a memory circuit and a data output circuit. The memory circuit outputs first internal data having a first burst length in a first mode and outputs the first internal data and second internal data in a second mode. A sum of the first and second internal data has a second burst length. The data output circuit outputs the first internal data as first output data through a first input/output line in the first mode. The data output circuit outputs the first internal data as the first output data through the first I/O line and outputs the second internal data as second output data through a second I/O line in the second mode. The data output circuit controls an internal current according to a logic level combination of the first and second internal data to generate the first and second output data in the second mode.