There is provided a semiconductor device which is simple in configuration and resistant to tampering. A user input unit receives an authentication code input by a user. A CPU determines whether a user's access is legal based on the input authentication code and activates an enable signal if the user's access is legal. A normal row decoder decodes the row address specified by the CPU and selects a normal memory cell of any row based on the result of decode. A redundancy row decoder prohibits the selection by the normal row decoder when the specified row address agrees with the row address of a predetermined normal memory cell only if the enable signal is activated and selects a redundant memory cell of any row.
