An image sensor uses a pixel circuit which includes a BJT phototransistor having multiple selectable beta values. The BJT is one semiconductor device includes: a substrate having a first conductivity type; a first well having the first conductivity type; a collector electrode having the first conductivity type in the first well; a second well having a first concentration of a second conductivity type; a first emitter electrode having the first conductivity type in the second well; a base electrode having the second conductivity type in the second well; a third well having a second concentration of the second conductivity type, wherein the second concentration is different from the first concentration; and a second emitter electrode having the first conductivity type in the third well.