Ion implantation is a widely used technique for the fabrication of high performance bipolar transistors giving good control of dose and junction depth. Precautions are normally taken to reduce the effects of axial channelling by orientating the slices off axis from the ion beam. The effects of planar channelling can also be significant however, particularly in the case of bipolar transistors where the result can be large variations in the gain of the transistors across the slice. This paper considers the causes of these variations and the ways in which they can be alleviated by modifying the transistor structure and by orientating the slices during the base implant.