The external shapes of tri-pyramid defects are summarized and typical shapes, deviations from the typical, and the interactions between tri-pyramids and stacking faults are described. Two basic types of typical tri-pyramids were observed, one with a single peak, and the other with three peaks. The symmetry of the typical tri-pyramids is three-fold. The angle between the apexes of the three pyramids composing the tri-pyramid is 120 °. Each of the pyramids composing the tri-pyramid is a single crystal but with crystallographic orientation different from that of the rest of the layer. The deviations consist of amputated tri-pyramids, bi-pyramids and mono-pyramids, none of which are symmetrical. The layer surface nearest the tri-pyramid is not planar, but distorted. Dash etch was used to reveal stacking faults interacting concentrically with typical tri-pyramids. The dimensions of the tri-pyramid and the stacking fault are proportional to the epitaxial layer thickness. Photographs of interactions among tri-pyramids and stacking faults are obtained by using S.E.M. to obtain high resolution, which reveals finer details in higher magnifications. Traces of SiC or SiO2 or other foreign materials, together with some basic mechanism, are probably responsible for tri-pyramid formation. They can be prevented by proper treatment of the silicon substrate prior to the layer growth.