Abstract The fcc(γ)→hcp(e) martensitic transformation in Fe–Mn–Si based shape memory alloys proceeds through a stacking fault mechanism. In the present paper, the symmetry characteristics of stacking faults are described by using the layer group theory, indicating that the intrinsic SF belongs to P 6 2m and the extrinsic fault to P321. The fault tetrahedron exhibits some sort of symmetry too. According to various repeating structures of the close-packed planes, transition states of the formed martensite are listed and exemplified. A thermodynamic method is proposed to calculate their chemical free energies and evaluate their stabilities which are in the order of 2H>4H>5H>6H>8H.