In this work, we investigated random telegraph signal (RTS) amplitude and the probability of trap empty along two different drain current directions for various gate lengths using novel test structures which enable to measure RTS in large numbers. Asymmetry of RTS amplitude along source-drain current direction increases as gate length shortens because a trap near the gate edge dominates RTS phenomenon as gate length shortens. The probability of trap empty shows weak positive correlation between both directions but asymmetric difference of that partially remains. We also investigated RTS characteristics dependence on kinds of gate insulator films and plasma damages of back-end-of-line (BEOL). Silicon oxynitride gate insulator film has bad effect on RTS and plasma damage does not appear as the increase of RTS amplitude up to 51,385 of antenna ratio.