Abstract-Segmented-channel MOSFETs (SegFETs) can achieve both good performance and variation robustness through the use of HfO 2 (a high-k material) to create the shallow trench isolation (STI) region and the very shallow trench isolation (VSTI) region in them. SegFETs with both an HTI region and a VSTI region (i.e., the STI region is filled with HfO 2 , and the VSTI region is filled with SiO 2 ) can meet the device specifications for high-performance (HP) applications, whereas SegFETs with both an STI region and a VHTI region (i.e., the VSTI region is filled with HfO 2 , and the STI region is filled with SiO 2 ) are best suited to low-standby power applications. AC analysis shows that the total capacitance of the gate (C gg ) is strongly affected by the materials in the STI and VSTI regions because of the fringing electric-field effect. This implies that the highest C gg value can be obtained in an HTI/VHTI SegFET. Lastly, the three-dimensional TCAD simulation results with three different random variation sources [e.g., line-edge roughness (LER), random dopant fluctuation (RDF), and work-function variation (WFV)] show that there is no significant dependence on the materials used in the STI or VSTI regions, because of the predominance of the WFV.