There is provided a bipolar transistor (with a respective fabrication method) that provides superior noise characteristics and gain diffusion. The fabricating method includes forming a first base region at a collector region, which in turn is formed on a substrate. A first silicon layer is formed on the base region, and a second silicon layer is formed on the first silicon layer using a forming method different from the method used in forming the first silicon layer. An emitter region is then formed from impurities at the base region by performing a thermal process.