Silicon bipolar transistors are described with common emitter current gains approaching 25 000, believed to be the highest ever reported for a bipolar device. A heterojunction emitter structure based on a tunneling metal-thin insulator-semiconductor (MIS) contact in conjunction with a shallow implanted base region is responsible for this improved performance. The significance of this result lies in the fact that it demonstrates advantages in both the injection efficiency of the emitter and the control of base properties which may lead to improved silicon bipolar transistor performance over a range of applications.