The structure of feedforward inverses is a fundamental problem in the invertibility theory of finite automata. The characterization of the structure of feedforward inverses with delay steps ≥3 is a long-term unsolved problem. This paper deals with this topic. For a binary weakly invertible semi-input memory finite automaton C(M_af ) with delay 3, where the state graph of M_a is cyclic, the characterizations of the structures are given when its minimal 3-output weight is 1, 2, and 8, respectively. Because C(M_af ) is weakly invertible with delay 3 iff it is weakly inverse with delay 3, a partial characterization of the structure of binary feedforward inverses with delay 3 is obtained.