A fault model in the state transition level of finite state machines is studied. In this model, called a single-state-transition (SST) fault model, a fault causes a state transition to go to a wrong destination state while leaving its input/output label intact. An analysis is given to show that a test set that detects all SST faults will also detect most multiple-state-transition (MST) faults in practical finite state machines. It is shown that, for a N-state M-transition machine, the length of the SST fault test set is upper-bounded by 2 × M × N2 while the length is exponential in terms of N for a checking experiment. Experimental results show that the test set generated for SST faults achieves not only a high single stuck-at fault coverage but also a high transistor fault coverage for a multilevel implementation of the machine.