  The effective g-factor of 2D holes in modulation doped \mbox{p-SiGe/Ge/SiGe}
structures was studied. The AC conductivity of samples with hole densities from
$3.9 \times 10^{11}$~to $6.2 \times 10^{11}~\text{cm}^{-2}$ was measured in
perpendicular magnetic fields up to $8~\text{T}$ using a contactless acoustic
method. From the analysis of the temperature dependence of conductivity
oscillations, the $\mathrm{g}_{\perp}$-factor of each sample was determined.
The $\mathrm{g}_{\perp}$-factor was found to be decreasing approximately
linearly with hole density. This effect is attributed to non-parabolicity of
the valence band.
