  We assume a generic real singlet scalar extension of the Standard Model
living in the vacuum $(v,w)$ at the electroweak scale with $v=246$ GeV and $w$
being respectively the Higgs and the singlet scalar vacuum expectation values.
By requiring {\it absolute} vacuum stability for the vacuum $(v,w)$, the
positivity condition and the perturbativity up to the Planck scale, we show
that the viable space of parameters in the model is strongly constrained for
various singlet scalar vacuum expectation values $w=0.1, 1, 10, 100$ TeV. Also,
it turns out that the singlet scalar mass can be from a few GeV up to less than
TeV.
