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AlGaAs/GaAs/GaAs and GaInP/GaAs/GaAs n-p-n heterojunction bipolar transistors (HBTs) are now in widespread use in microwave power amplifiers. In this paper, improved HBT structures are presented to address issues currently problematic for these devices: high offset and knee voltages and saturation charge storage. Reduced HBT offset and knee voltages (VCE,os and Vk) are important to improve the power amplifier efficiency. Reduced saturation charge storage is desirable to increase gain under conditions when the transistor saturates (such as in over-driven Class AB amplifiers and switching mode amplifiers). It is shown in this paper that HBT structures using a 100-Å-thick layer of GaInP between the GaAs base, and collector layers are effective in reducing VCE,os to 30 mV and Vk measured at a collector current density of 2×104 A/cm2 to 0.3 V (while for conventional HBTs VCE,os=0.2 V and Vk=0.5 V are typical). A five-fold reduction in saturation charge storage is simultaneously obtained.