As technology scales, the protection of Finite State Machines' (FSMs) states against single event upset (SEU) and multiple bit upsets (MBUs) becomes more difficult. In this paper, a self-checking approach to enhance the SEU/MBUs immunity of FSMs' states by replicating One-Hot code times for state encoding is presented. This approach can correct less than bit-flip faults in the state register per cycle. Bit-flips are treated as random events and modeled by applying Poisson distribution. Two characteristics of this approach are obtained through probability analysis: first, this approach performs better with the increase of , whereas worse when an FSM contains more states; second, this approach can offer more enhanced reliability than Binary or One-Hot state encoding with Triple Modular Redundancy (TMR). The former characteristic leads to the further improvement of this approach which is called state-reforming. The reliabilities of this proposed approach and its state-reformed solutions, as well as are all evaluated through simulations of fault injections.