Low frequency (LF) noise is a powerful and nondestructive technique for evaluating the oxide-semiconductor interface and an effective evaluating tool in characterizing electronic device's structure and reliability. In this study, we present a systematic analysis of the striking abnormal 1/f noise behavior of the hot carrier induced defects in highspeed polysilicon emitter bipolar transistors (PE-BJTs) and SiGe HBTs. Here, the comparative results before and after hot carrier degradation reveal that low frequency noise spectra are not correlated with the density and distribution of the interfacial defects, which related to Si dangling bonds reside at the SiO2/Si interface in PE-BJTs and SiGe HBTs.