In this work, we statistically study characteristic fluctuation of 16-nm-gate high-κ/metal gate (HKMG) MOSFETs by random-discrete-dopants (RDDs) inside silicon channel and random-interface-traps (RITs) at high-κ/silicon interface. Randomly generated devices with three-dimensional (3D) RDDs inside device channel and 2D RITs at HfO 2/Si interface are incorporated into quantum-mechanically corrected 3D device simulation. Device characteristics, as influenced by different degrees of fluctuation, are discussed in relation to RITs near the source and drain ends, and RDDs near the device channel surface and silicon substrate. Characteristic fluctuations are affected to different extents by the random combinatorial RDDs and RITs. Nonlinearly correlated RDDs and RITs further violate the statistical assumption of independent identical distributions between the RDDs- and RITs-induced random variables. Consequently, for the studied 16-nm-gate HKMG MOSFETs, the threshold voltage fluctuation induced by the combined RDs and ITs is less than their statistical sum due to local interaction of surface potentials resulting from the RDDs and RITs simultaneously. In contrast to RDDs fluctuation, the screening effect of device's inversion layer cannot effectively screen potential's variation resulting from RITs; thus, devices still have noticeable gate capacitance characteristic fluctuation under high gate bias.