Abstract: A bipolar semiconductor device with interdigitated emitter and base regions has a sub-region of the base, which has a shorter carrier recombination time than the major part of the base region due to the presence of argon ion implantation induced carrier recombination centers. The sub-region of the base is located centrally with respect to the emitter region to intercept the transient current lines during device turn-off and so to promote collapse of the transient current and the avoidance of second breakdown of the device. The centrally located sub-region of the base is remote from the emitter region edges to collector region current flow when the device is on. The ions may be implanted at energies between 50 keV and 3 MeV and at doses between 10.sup.11 ions cm.sup.-2 and 10.sup.14 ions cm.sup.-2. The implanatation mask may be provided by photolithographically processed resist having a thickness between 0.5 .mu.m and 4 .mu.m dependant on the ion implantation energy.