A semiconductor device, includes an input buffer, first and second PMOS transistors serially interconnected between a first power supply node and an output node of the input buffer. First and second NMOS transistors are serially interconnected between a second power supply node and the output node of the input buffer. A replica circuit includes a third and fourth PMOS transistors serially interconnected between the first power supply node and an output node of the replica circuit. Third and fourth NMOS transistors are serially interconnected between the second power supply node and the output node of the replica circuit. The input node of the replica circuit is connected to the output node of the replica circuit and a comparison circuit compares a voltage at the output node of the replica circuit to a reference voltage.