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Manipulation of spin information in semiconductors has been the topic of both experimental and theoretical studies. In this paper, the theoretical compact models for the spin-relaxation length (SRL) in nondegenerately doped silicon and gallium arsenide are presented. These models account for the impact of impurity doping and phonons on mediating spin relaxation. In addition, the models are exhaustively calibrated with the published experimental data. It is shown that the SRL at room temperature in Si drops from 5 to 1 μm as the doping increases from 1014 to 1019 cm-3. However, the SRL in GaAs is independent of doping for nondegenerate doping levels. While the rolloff of the SRL with temperature in Si depends upon the doping concentration, the rolloff of the SRL for nondegenerately doped GaAs is doping independent and proceeds as T-1, where T is the operating temperature. The models of the SRL in conjunction with spin drift-diffusion equation are used to study the steady-state spin transport in both the conventional and nonlocal semiconducting spin-valve geometries. The presence of an electric field leads to a clear enhancement of spin injection and transport efficiency in the conventional spin-valve geometry. The degradation in the spin injection and transport efficiency with the channel length is much steeper in nonlocal spin valves as compared to that in the conventional spin valves.