This paper analyzes the amplitude of Random Telegraph Noise (RTN) caused by a single trap in the silicon film of UTBOX devices by two-dimensional (2-D) numerical simulations. The dependence of the relative RTN amplitude on the bias condition and trap position is simulated, explaining the large variability of the RTN amplitude. The simulated traps close to the source or drain have an asymmetric VD dependence, which is in good agreement with the reported experimental data. This implies that the asymmetry of the VD dependence of switched source and drain can be utilized to identify the lateral trap position. The underlying reasons for the voltage dependence are analyzed and it is shown that the electric field where the trap is located has a reciprocal relationship with the relative RTN amplitude.