  We determine the energy splitting of the conduction-band valleys in
two-dimensional (2D) electrons confined in silicon metal oxide semiconductor
(Si-MOS) Hall-bar transistors. These Si-MOS Hall bars are made by advanced
semiconductor manufacturing on 300 mm Si wafers and support a 2D electron gas
of high quality with a maximum mobility of 17.6$\times$10$^3$cm$^2$/Vs and
minimum percolation density of 3.45$\times$10$^{10}$cm$^{-2}$. Because of the
low disorder, we observe beatings in the Shubnikov-de Haas oscillations that
arise from the energy-split two low-lying conduction band valleys. From the
analysis of the oscillations beating patterns up to T = 1.7 K, we estimate a
maximum valley splitting of 8.2 meV at a density of
6.8$\times$10$^{12}$cm$^{-2}$. Furthermore, the valley splitting increases with
density at a rate consistent with theoretical predictions for a near-ideal
semiconductor/oxide interface.
