A 1/2[0001](0001) stacking fault and a planar 60° rotational domain boundary on the (0001) plane in as-grown CVD α-Si3N4 crystals have been characterized by high-resolution electron microscopy and image simulation. As reported previously, two types of coherent boundaries have been observed in this material, namely, stacking faults and rotational domain boundaries. The former involves only a translational displacement, while the latter separates two grains by a 60° rotation in addition to a translation. Inasmuch as the difference resulting from the rotational component can hardly be detected by high-resolution electron microscopy, care must be taken to analyze them first by analytical electron microscopy. In this paper, these two types of boundaries are studied and structural models are constructed that give simulated images in satisfactory agreement with observed images.