Using 3-D technology computer aided design simulation, we investigated the impact of equivalent oxide thickness (EOT) on threshold voltage (V-TH) variation induced by work-function variation (WFV) in multigate devices. The WFV-induced VTH variation in multigate devices does not significantly vary with the dielectric constant of the gate dielectric material, but increases with decreasingphysicaloxide thickness(T-OX). As T-OX becomes thinner, electric field tends to be locally concentrated, causing a large variation of electrostatic potential in channel. The slope of the ratio of average grain size to gate area (RGG) plot is observed with various oxide thicknesses. It is confirmed that we can alleviate the WFV-induced VTH variation without significant performance degradation if gate dielectric layer becomes thicker with appropriately adopted higher-k engineering. In addition, the impact of EOT (including interface layer) on the WFV-induced VTH variation is studied.