  We have calculated formation enthalpies, band gaps, and natural band
alignment for $\rm MgO_{1-x}S_{x}$ alloys by first principles calculation based
on density functional theory. The calculated formation enthalpies show that the
$\rm MgO_{1-x}S_{x}$ alloys exhibit a large miscibilitygap, and a metastable
region was found to occur when the S content was below 18% or over 87%. Effect
of S incorporation for band gaps of $\rm MgO_{1-x}S_{x}$ alloys shows large
bowing parameter (b $ \simeq $ 13 eV) induced. The dependence of the band
lineup of $\rm MgO_{1-x}S_{x}$ alloys on the S content by using two different
methods, and the change in the energy position of valence band maximum (VBM)
was larger than that of conduction band minimum. Based on the calculated VBM
positions, we predicted that $\rm MgO_{1-x}S_{x}$ with S content 10 to 18% can
be surface charge transfer doping by high electron affinity materials. The
present work provides an example to design for p-type oxysulfide materials.
