In modern high performance analog integrated circuits, 1/f noise is one of the key issues affect the circuit performance. The effects of emitter structure on DC and low frequency noise characteristics in double polysilicon self-aligned high speed complementary NPN bipolar transistors was studied. It was demonstrated that the interfacial oxide layer between polysilicon emitter and monocrystalline silicon and the emitter geometry were the major factors which greatly affect the 1/f noise characteristics.