In this paper, we analyze the structure of trenched source/drain that boosts the on-current in 5 nm node single and stacked nanowire field effect transistors (NWFET). When the sheet resistivity between contact and source/drain is low, the trenched contact increases the contact area and decreases the contact resistance, which is very ineffective. When the sheet resistance is high, however, the profit from trenching the source/drain is higher than the profit from the strain engineering. Also, in the case of single nanowire FET, because the height of the raised source/drain is small, the effect of the on-current boosting with the trenched source/drain is smaller than the strain effect. However, the source/drain can be trenched deeply in stacked nanowire FET. In that case, the on-current boosting with the trenched source/drain is larger than that with channel strain engineering.