A material made by arranging layers of gallium-arsenide-antimonide (GaAs.sub.xSb.sub.1-x, 0.0.ltoreq.x.ltoreq.1.0) and/or indium-gallium-arsenic-nitride (In.sub.yGa.sub.1-yAs.sub.zN.sub.1-z, 0.0.ltoreq.y, z.ltoreq.1.0) in a specific order is used to form the transistor base of a heterojunction bipolar transistor. By controlling the compositions of the materials indium-gallium-arsenic-nitride and gallium-arsenide-antimonide, and by changing the thickness and order of the layers, the new material would possess a specific energy gap, which in turn determines the base-emitter turn-on voltage of the heterojunction bipolar transistor.