  Single-electron pumps based on semiconductor quantum dots are promising
candidates for the emerging quantum standard of electrical current. They can
transfer discrete charges with part-per-million (ppm) precision in nanosecond
time scales. Here, we employ a metal-oxide-semiconductor silicon quantum dot to
experimentally demonstrate high-accuracy gigahertz single-electron pumping in
the regime where the number of electrons trapped in the dot is determined by
the thermal distribution in the reservoir leads. In a measurement with
traceability to primary voltage and resistance standards, the averaged pump
current over the quantized plateau, driven by a \mbox{$1$-GHz} sinusoidal wave
in the absence of magnetic field, is equal to the ideal value of $ef$ within a
measurement uncertainty as low as $0.27$~ppm.
