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The pre- and post-irradiation effects on the DC electrical characteristics of 100 MeV Phosphorous (P7+) and 80 MeV Nitrogen (N6+) ion-irradiated NPN transistors were studied in the dose range from 600 krad (Si) to 100 Mrad (Si). The different electrical characteristics, such as Gummel characteristics, excess base current (ΔIB = IB-Post – IB-Pre), current gain (hFE), damage constant (K) and output characteristics, were measured in situ after ion irradiation. The considerable increase in the base current (IB) at lower VBE and slight decrease in the collector current (IC) at higher VBE were observed after ion irradiation. The C–V measurements revealed that the doping concentration (Nd) was found decreased, while the built-in potential (Vbi) increased after irradiation. The ion-irradiated results are compared with 60Co gamma-irradiated results in the same dose range. The SRIM simulation was performed to understand the range of ions and energy loss in the transistor structure. The SRIM simulation showed that 100 MeV P7+ and 80 MeV N6+ ions can easily pass through the active region of transistors by creating ionization and displacement damages in the device structure. The irradiation results showed that ions induce more degradation in the electrical characteristics when compared to 60Co gamma radiation at the same dose range. [ABSTRACT FROM AUTHOR]