We have extensively investigated transport properties of nanowire MOSFETs and single-electron/single-hole transistors by experiments and band calculations. Special focus has been placed on measurements and physics of the channel direction dependence and charge polarity dependence. We adopted a special device structure with a common n-type and p-type channel. We confirmed that a -directed nanowire p-type FET has the smallest
fluctuations caused by the size variations. We also verified that a -directed single-hole transistor is the best device for the single-charge transistor operations. Actually, we observed Coulomb blockade oscillations with the record high peak-to-valley-current ratio of 480 at room temperature in a  single-hole transistor.