A security circuit for a semiconductor memory, is disclosed, which is able to provide excellent security and safety for data stored in the memory, even if a small number of pads are available. The circuit includes a pad connected to a terminal on a memory IC for use as a write enable terminal, a fuse connected between the pad and the internal memory IC for isolating the internal memory IC from the pad after data is written on the memory IC, a low voltage detecting part for detecting a low voltage at a pad terminal, a latching part for forwarding an output of the low voltage detecting part after maintaining or inverting the output, a switching part for supplying power sufficient to the fuse in response to a signal from the latching part, a pull-up part for pulling up a voltage of the memory when the fuse is blown, and a power on reset part for initializing the latching part.