The work-function fluctuation (WKF) in 16-nm single- and triple-fin field effect transistors (FETs) with different aspect ratio (AR) of device geometry is for the first time explored. The influences of grain size of metal gate and AR on σIoff/ σIon are drawn; the device with high AR and large number of silicon fin can suppress the WKF. The triple-fin FinFET (AR = 2) is superior to triple-fin tri-gate (AR = 1) and quasi-planar (AR = 0.5) structures, where gate materials TiN and MoN are considered in n- and p-typed FETs. Compared with nFET, the WKF of pFET is larger than that of n-typed device due to the gate material having wider work-function variation. The 3D device simulation study on WKF-induced σIoff/ σIon benefits fabrication of nulti-fin devices.