Microtwin lamellae and tri‐pyramid defects often form in {111} silicon epitaxial films and these are affected by impurities within the substrate and system. The tri‐pyramids, which are doubly twinned with respect to the substrate surface, result when three oblique pyramids sprout from a triangular twinned deposit which forms on the (111) substrate surface. Twinning enhanced by adsorbed impurities could account for the initial twinning, but since it is a random process, cannot explain the second twinning operation for all three pyramids. The results also show that SiC platelets are not unique or necessary for tri‐pyramid formation. A reentrant twin mechanism is proposed to account for this as the twinned islands join up with correct ones. This mechanism can also account for the formation of microtwin lamellae which often accompany the tri‐pyramids. It is also shown that oblique microtwin lamellae can propagate directly from the twinned deposits and that multiple twin lamellae can result when the twinned deposit has steps in it.