Current fluctuations with discrete levels, which are called random telegraph signals (RTSs), have been studied in small size metal‐oxide‐semiconductor field‐effect transistors (MOSFETs) from both viewpoints of relative current change and of correlated switchings. A large relative current change of as much as 30% has been observed, even at room temperature. It behaves similarly as normal small RTSs in terms of statistics and temperature dependence. RTSs have been found also in 20‐&mgr;m channel width MOSFETs. These results require another mechanism to explain RTSs in addition to simple Coulomb scattering or number fluctuation. It is emphasized that an interaction between defects at the Si/SiO2interface is necessary to understand the correlated RTSs. The experimental results are reasonably reproduced by a model calculation assuming interacting defects. It is also pointed out that new RTSs generated by electrical stress might be a serious concern in lower submicron devices.