Self-heating effects (SHE) in nanowire transistors (NW Tr.) have been systematically studied with respect to the dependence on the NW width (W), NW height (H), and gate length (Lg). Temperature rise (ΔT) by SHE in NW Tr. is smaller than SOI planar Tr. when compared with power consumption per unit area. Instead, ΔT at the same total power consumption (not normalized by area) is independent of W, H and Lg in sub-100nm regions, since the heated area does not scale with Lg and W. Drain current (Id) reduction by SHE is almost constant for a wide range of Lg due to the weak temperature dependence of Id in velocity saturation regime. Id reduction in narrow NW Tr. is slightly less than that in wide NW Tr. because of the st