P-type second semiconductor layers each interposed between a corresponding pair of n-type first semiconductor layers reduce the apparent doping concentration in the entire collector layer without reducing the doping concentrations in the first semiconductor layers. This improves the linearity of capacitance characteristics and enables sufficient mass productivity to be achieved. Interposing each of the second semiconductor layers between the corresponding pair of the first semiconductor layers reduce the average carrier concentration over the entire collector layer, which allows a wide depletion layer to be formed inside the collector layer and, as a result, reduces base-collector capacitance.