We studied the relation between body effect factor and subthreshold slope in ultra-thin buried oxide tri-gate nanowire MOSFETs with various gate lengths, nanowire widths, and nanowire heights. As gate length decreases, body effect factor increases due to the enhancement and suppression of the short channel effect with positive and negative back gate bias voltage, respectively. The reduction of nanowire width leads to the decrease in both body effect factor and subthreshold slope resulting in trade-off relation, whereas better subthreshold slope and larger body effect factor were achieved by thinning nanowire height. (C) 2013 Elsevier Ltd. All rights reserved.