A random code generator is installed in a semiconductor chip and includes a PUF cell array, a control circuit and a verification circuit. The PUF cell array includes m×n PUF cells. The control circuit is connected with the PUF cell array. While a enroll action is performed, the control circuit enrolls the PUF cell array. The verification circuit is connected with the PUF cell array. While a verification action is performed, the verification circuit determines that p PUF cells of the PUF cell array are normal PUF cells and generates a corresponding a mapping information, wherein p is smaller than m×n. While the semiconductor chip is enabled, the control circuit reads states of the p normal PUF cells of the PUF cell array according to the mapping information and generates a random code according to the states.