Methodology for accurate extrapolation of InGaP/GaAs HBT safe operating area (SOA) for variations in emitter area and ballast resistor size.

•SOA for multi-finger InGaP/GaAs HBTs follows ICE=AVCE−B dependence with B∼1.9.•Current collapse is mitigated by emitter ballast resistors to increase SOA.•Emitter ballast resistor and total emitter area most important for setting SOA.•A for new HBT layouts calculated accurately by linear extrapolation of area and Rb.