HETEROJUNCTION BIPOLAR TRANSISTOR

PROBLEM TO BE SOLVED: To enable inhibition of inter-valley scattering that leads to performance deterioration of a heterojunction bipolar transistor in a state capable of practical manufacturing.SOLUTION: A heterojunction bipolar transistor comprises a third collector layer 123 which is formed between a first collector layer 121 and a second collector layer 122 and composed of a group III-V compound semiconductor. Here, conduction band edge energy of the third collector layer 123 is set smaller than conduction band edge energy of the first collector layer 121 at a junction interface between the first collector layer 121 and the third collector layer 123. At the same time, conduction band edge energy of the third collector layer 123 is set smaller than conduction band edge energy of the second collector layer 122 at a junction interface between the second collector layer 122 and the third collector layer 123.