We report measurements of spin-dependent scattering of conduction electrons by neutral donors in accumulation-mode field-effect transistors formed in isotopically enriched silicon. Spin-dependent scattering was detected using electrically detected magnetic resonance where spectra show resonant changes in the source-drain voltage for conduction electrons and electrons bound to donors. We discuss the utilization of spindependent scattering for the readout of donor spin-states in silicon based quantum computers. Neutral impurity scattering is spin-dependent because different spin configurations of the conduction and donor electrons (singlet or triplet) imply a different spatial distribution of the two-electron wavefunction, which translates into a difference in scattering crosssections. This SDS process by phosphorus impurities in an accumulation-mode fieldeffect transistor (aFET) was first observed by Ghosh and Silsbee using electrically detected magnetic resonance (EDMR) [9]. In an EDMR experiment, a static magnetic field induces a Zeeman splitting in the electron energy levels, and in thermal equilibrium, triplet scattering is favored as more spins are aligned with the static field. Singlet scattering can be enhanced by inducing spin flips with a resonant microwave field. This increase in singlet content then registers as an effective channel resistance change of the 3 aFET. Ghosh and Silsbee used large-area aFETs (1×0.1 mm 2 ) formed in bulk-doped silicon with about 2×10 17 phosphorus/cm 3 [9]. The number of donors close (~10 nm) to the aFET channel that contribute to SDS was estimated to be ~10 8 . However, bulk donors far away from the channel that did not contribute to SDS caused an undesired bolometric signal due to resonant microwave absorption, and substantial efforts were undertaken to resolve interfering bolometric effects and to isolate the SDS signal.In the present work, we demonstrate SDS by neutral 121 Sb donors in silicon aFETs. In order to avoid bolometric signals, aFETs were formed in undoped silicon and ~6×10 6 donors were implanted into the transistor channel. While most donor-based silicon quantum computer proposals have suggested spins of 31 P as qubits, 121 Sb is used in our experiments due to its smaller straggling in the channel implantation process, lower diffusion rates in silicon, and to avoid spurious signals arising from residual background 31 P atoms in the silicon substrate or from the polycrystalline silicon gate.