A semiconductor device includes a section signal generator and a decoder. The section signal generator generates a section signal by retarding a pre-section signal including a pulse created during a read operation or a write operation by a delay time that is set according to a level combination of first and second test mode signals. The decoder decodes address signals in response to a pulse of the section signal to generate column selection signals, one of which is selectively enabled, to store an external data in a memory cell of an internal circuit or to output a data stored in a memory cell of an internal circuit.