A method of forming an isolation region using porous silicon and a related structure are disclosed. One embodiment of the method may include forming a collector region; forming a porous silicon region in the collector region; forming a crystalline silicon intrinsic base layer over the collector region, the intrinsic base layer extending over a portion of the porous silicon region to form an extrinsic base; and forming an isolation region in the porous silicon region. The method is applicable to forming an HBT having a structure including a crystalline silicon intrinsic base extending beyond a collector region and extending over an isolation region to form a continuous intrinsic-to-extrinsic base conduction path of low resistance. The HBT has improved performance by having a smaller collector to intrinsic base interface and larger intrinsic base to extrinsic base interface.