We investigated the effect of spin drift on spin accumulation in highly doped silicon (Si) by using a non-local three-terminal (NL-3T) and four-terminal (NL-4T) methods, and have clarified that the spin accumulation voltages in a NL-3T device were modulated due to spin drift and that spin lifetime can be accurately extracted by employing a modified spin drift-diffusion equation. The extracted spin lifetime is 4-7 ns, which is slightly shorter than the intrinsic spin lifetime (8 ns) measured in the NL-4T method in the same Si device because of spin drift. It is elucidated that the spin drift effect should be considered for the precise estimation of spin lifetime in Si by NL-3T method. © 2012 American Institute of Physics.