A semiconductor wafer and its manufacturing method are provided where the current driving capability of a MOS transistor can be sufficiently enhanced. An SOI layer wafer in which an SOI layer (32) is formed has a crystal direction notch (32a) and a crystal direction notch (32b). The SOI layer wafer and a supporting substrate wafer (1) are bonded to each other in such a way that the notch (32a) and a crystal direction notch (1a) of the supporting substrate wafer (1) coincide with each other. When bonding the two wafers by using the notch (32a) and the notch (1a) to position the two wafers, the other notch (32b) of the SOI layer wafer can be engaged with a guide member of the semiconductor wafer manufacturing apparatus to prevent positioning error due to relative turn between the wafers. Thus an MOS transistor with a sufficiently improved current driving capability can be fabricated on the semiconductor wafer with the two wafers positioned in crystal directions shifted from each other.