We have investigated temperature dependence of the longitudinal conductivity $σ_{xx}$ at integer filling factors $ν =i$ for Si/SiGe heterostructure in the quantum Hall effect regime. It is shown that for odd $i$, when the Fermi level $E_{F}$ is situated between the valley-split levels, $Δ σ_{xx}$ is determined by quantum corrections to conductivity caused by the electron-electron interaction: $Δσ_{xx}(T)∼ \ln T$. For even $i$, when $E_{F}$ is located between cyclotron-split levels or spin-split levels, $σ_{xx}∼ \exp[-Δ_{i}/T]$ for $i=6,10,12$ and $∼ \exp [-(T_{0i}/T)]^{1/2}$ for $i=4,8$. For further decrease of $T$, all dependences $σ_{xx}(T)$ tend to almost temperature-independent residual conductivity $σ_{i}(0)$. A possible mechanism for $σ_{i}(0)$ is discussed. Comment: 6 pages, 8 figures (included), accepted in Phys. Rev. B