A bipolar transistor and a method of fabricating the same are provided which are adapted to reduce chip size and production costs. To produce the transistor, a second conductive type well region is formed in a first conductive type semiconductor substrate and isolation trenches are formed at both sides of the well region. A high density second conductive type buried layer is formed in the semiconductor substrate which is formed at the bottom of the isolation trench. The buried layer is formed in two regions surrounding respective bottoms of two adjacent isolation trenches. The two regions are electrically connected with each other and in direct contact with the well region. An extrinsic base region and a device isolation region are formed sequentially onto the semiconductor substrate using a nitration layer pattern as a mask, wherein the nitration layer pattern is formed on the surface of semiconductor substrate. An intrinsic base region is formed into the well region and an emitter region into the intrinsic base region using the device isolation layer as a mask. The bipolar transistor and method of fabrication can reduce the chip size, the production costs, and the resistance of the collector by forming the isolation trench, wherein the isolation trench is used to form the buried layer and functions as a sink layer (collector layer). The process provides self-alignment of the extrinsic base region, the intrinsic base region, and the emitter region to reduce process scattering.