Abstract: The peripheral boundary of a plane pn junction of a semiconductor device, for example, the base-collector junction of a transistor, that is required to withstand high reverse voltages in operation of the device is defined by a channel having a side-wall defining the peripheral boundary of the junction. The channel is formed by firstly mechanically cutting a desired contour channel into a surface of a semiconductor body which has the junction formed therein. The channel is then subjected to chemical etching to remove semiconductor material damaged as a result of the mechanical cutting step and the channel is filled with an insulating glass to provide a protective coating over the pn junction and prevent contamination of the junction by a subsequently applied epoxy resin encapsulant for the device.