A method for forming a self-aligned bipolar transistor includes the steps of combination etching a silicon substrate in an opening to form a concave surface on the silicon substrate, and forming an intrinsic base and an associated emitter on the concave surface. The combination etching includes an isotropic etching and subsequent wet etching. The concave surface increases the distance between the external base for the intrinsic base and the emitter to thereby increase the emitter-base breakdown voltage.