The structure of YBa2Cu3Oxthin films and YBa2Cu3Ox/PrBa2Cu3Oxsuperlattice films grown on (00L) SrTiO3substrates has been studied using x‐ray diffraction and transmission electron microscopy. The films consist of four symmetry‐equivalent domains related by mutually perpendicular (hh0) and (hh¯0) twin boundaries. One twin orientation is often highly favored over the other. We have correlated this in‐plane symmetry breaking with small miscuts of the substrate surface towards the [HH0] direction and propose that interfacial steps act as nucleation sites for twins. Thus, by controlling the surface normal, a technique is described for producing films containing aligned twin boundaries.