For the first time (In,Ga)As/InP n-p-n heterojunction bipolar transistors (HJBT's) applicable to integrated circuits have been fabricated by triple ion implantation. The base has been formed by beryllium ion implantation and the collector by silicon ion implantation. The implants were made into an LPE-grown n-n (In,Ga)As/InP heterostructure on an n+-InP substrate. This inverted mode emitter-down heterojunction transistor structure demonstrates to a maximum current gain of 7 with no hysteresis in the characteristics. The ideality factors of the IBversus VBE, and ICversus VBEcharacterisitics with VCB= 0, are 1.25 and 1.08, respectively, indicating that the defect level in the herterojunction is low and that minority-carrier injection and diffusion is the dominant current flow mechanism.