High beta, high frequency transistors require very narrow and high resistance base structures, thereby placing a low limit of collector-emitter voltages that may be used without encountering "punch-through" breakdown. This invention permits the use of normal collector-emitter voltages without danger of punch-through problems by injecting into the high resistance base material an impurity grid that serves both as an electrostatic shield to increase the voltage breakdown level, and as a means of reducing the apparent lateral base resistance, thereby further increasing the high frequency capability of the device without degrading the high beta characteristics.