In this paper, compact semi-empirical models of spin-transport parameters in Si and GaAs as a function of doping concentration, temperature, and size effects are developed. It is found that the room-temperature spin-relaxation length, Ls, in n-type Si degrades from 5 μm at low doping levels to <1 μm for a doping level of 1019 cm3. On the other hand, Ls is 0.5 μm in GaAs at R.T., and it is independent of doping concentration but it degrades as 1/T, where T is the lattice temperature. Using the models of spin-transport parameters, the spin injection and transport efficiency (SITE) in non-local spin-torque (NLST) devices is quantified. It is found that there is an optimal doping concentration in Si that maximizes SITE. In the case of GaAs, SITE improves with increasing doping concentration due to the reduction in the resistivity with doping. The compact spin-transport models developed in this work can be used to estimate the performance and the energy dissipation of the NLST logic.