A heterojunction bipolar transistor is fabricated by stacking a Si collector layer, a SiGeC base layer and a Si emitter layer in this order. By making the amount of a lattice strain in the SiGeC base layer on the Si collector layer 1.0% or less, the band gap can be narrower than the band gap of the conventional practical SiGe (the Ge content is about 10%), and good crystalline can be maintained after a heat treatment. As a result, a narrow band gap base with no practical inconvenience can be realized.