Values of intrinsic carrier density ni in Ge1−xSnx alloy (0 ≤ x ≤ 0.2) are calculated by including composition dependent effective masses in Γ and L valleys in the conduction band, in light hole (LH) and heavy hole (HH) valence bands, and composition-dependent band gaps. The maximum temperatures of operation of the alloys are also determined over a range of dopant densities and alloy compositions. The temperature dependence of intrinsic density around room temperature is obtained by using x-dependent α and β parameters in Varshney’s equation. The maximum achievable electron mobility based on ni is estimated. © 2021, Springer Nature Singapore Pte Ltd.