  We experimentally demonstrate a Si spin metal-oxide-semiconductor
field-effect transistor (MOSFET) that exhibits a high on/off ratio of
source-drain current and spin signals at room temperature. The spin channel is
non-degenerate n-type Si, and an effective application of gate voltage in the
back-gated structure allows the spin MOSFET operation. This achievement can
pave the way to practical use of the Si spin MOSFET.
