Single-crystalline Co₂MnSi Heusler alloy films have been grown on GaAs(001) substrates by pulsed laser deposition (PLD). The best crystallographic quality of the Co₂MnSi films has been achieved after deposition at 450 K. The films exhibit in-plane uniaxial magnetic anisotropy with the easy axis of magnetization along the [1-10] direction superimposed with a fourfold anisotropy with the easy axis along <110>. Spin-resolved photoemission measurements of the single-crystalline Co₂MnSi films reveal a spin-resolved density of states that is in qualitative agreement with recent band structure calculations. The spin polarization of photoelectrons close to the Fermi level is found to be at most 12%, in contrast to the predicted half-metallic behavior. We suggest that these discrepancies may be attributed to a partial chemical disorder in the Co₂MnSi lattice.