As the dimensions of semiconductor devices are reduced, changes in the structure of the devices can have a pronounced effect on their electrical parameters. In some cases it may no longer be correct to assume that the electrical parameters can simply be scaled with device area. In the present study it will be shown that when polysilicon‐emitter bipolar transistors are reduced to submicron dimensions, shadowing of the ion implant into the emitter sidewalls can alter the dopant concentration in the polysilicon diffusion source, thereby changing the dopant profiles in the single‐crystal silicon, and hence the junction depths. This shadowing effect, although present in all devices, is only found to affect the electrical parameters of transistors when the emitter size approaches submicron dimensions.