Drain-induced barrier lowering (DIBL) is crucial in many applications of silicon nanowire transistors. This paper determined the effect of the dimensions of nanowires on DIBL. The MuGFET simulation tool was used to investigate the characteristics of the transistors. The transfer characteristics of transistors with different dimensions were simulated. The results show that longer nanowires with smaller diameters and lower oxide thickness decrease DIBL and tend to possess the best transistor characteristics.