In this paper electrical and thermal conductivity coefficients of heavily doped n-Silicon have been derived based on parabolic and modified density of states having band tails. The derivation uses Boltzmann transport equation with relaxation time arising from ionized impurity scattering mechanism as a dominant scattering mechanism compared to the phonon scattering mechanism where the calculations are made at room temperature. Note that semi-classical and quantum mechanics treatments are employed during discussion of scattering mechanisms and calculation of transport coefficients for parabolic and modified density of states having band tails considerations. There is significant variation of electrical and thermal conductivity as well as Weidman-Franz ratio as much as 30%, 101.86%, and 0.66% respectively.