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This paper presents a quantitative study on the device design for the control of threshold-voltage and the suppression of short-channel effects (SCEs) in ultrathin strained-silicon-on-insulator (strained-SOI) CMOSFETs in the sub-100-nm regime. A two-dimensional device simulation is used for this purpose, with emphasis on the impact of band offset in Si/SiGe heterostructures. For the control of threshold-voltage, the combination of the gate work function and the back gate bias is needed to obtain appropriate values of threshold-voltage in n- and p-channel MOSFETs and to suppress SiGe buried channels in p-channel MOSFETs with thicker strained-Si layers. Regarding SCEs, the importance and the necessity of thin SiGe layers are pointed out from the viewpoint of the influence of the higher permittivity of SiGe layers. It is shown that the SCEs of strained-SOI MOSFETs with thinner SiGe layers are almost the same level as those of unstrained-SOI.