  We propose a tight-binding (TB) model, that includes spin-orbit coupling
(SOC), to describe the electronic properties of methyl-substituted germanane
(GeCH$_3$). This model gives an electronic spectrum in agreement with first
principle results close to the Fermi level. Using the $\mathbb{Z}_2$ formalism,
we show that a topological phase transition from a normal insulator (NI) to a
quantum spin Hall (QSH) phase occurs at 11.6\% biaxial tensile strain. The
sensitivity of the electronic properties of this system on strain, in
particular its transition to the topological insulating phase, makes it very
attractive for applications in strain sensors and other microelectronic
applications.
