In this paper, the random telegraph noise (RTN) statistics in silicon nanowire transistors (SNWTs) are comprehensively studied. The capture/emission time constants and probabilities are found to be strongly impacted by the quantum confinement in SNWTs, which cannot be fully explained by classical RTN theory. A full quantum RTN model for SNWTs is proposed for fundamental understanding of the experiments. The characteristics of non-stationary RTN in SNWTs under high-field biases are studied for the first time, based on the developed statistical trap-response (STR) characterization method. The trap capture probability is found to be much different from that of the quasi-stationary RTN, leading to large errors in circuit aging prediction if using traditional RTN distributions. These new understandings are critical for robust SNWT circuit design against RTN.