A two-step source/drain elevated epitaxial process for ultra thin fully depleted (FD) silicon-on-insulator (SOI) metal–oxide–semiconductor field-effect transistors (MOSFETs) is proposed. The relation between the crystal quality of the source/drain extension regions and channel orientation with the silicon epitaxial process is analyzed by transmission electron microscopy (TEM). No defect is observed in the source/drain extension regions on the <100> channel, whereas crystal defects are observed on the <110> channel. Crystal defect generation in the source/drain extension regions is closely related to channel orientation. Moreover, a low parasitic resistance of thin-body SOI MOSFETs is realized in <100> channel SOI-MOSFET, and high Ion(Ids)–Ioff characteristics and the suppression of the roll-off characteristics of thin-body SOI MOSFETs with the <100> channel orientation are shown. It is confirmed that thin-body SOI MOSFETs with a two-step source/drain elevated epitaxial process have a high potential for the application in the 22 nm generation.