We have obtained Anti-Phase Boundary (APB) free GaAs epilayers on “quasi-nominal” (001) silicon substrates, while using a thick germanium strain relaxed buffer between the GaAs layer and the silicon substrate in order to accommodate the 4% lattice mismatch between the two. As silicon (001) substrates always have a small random offcut angle from their nominal surface plane, we call them “quasi-nominal.” We have focused on the influence that this small (≤0.5°) offcut angle has on the GaAs epilayer properties, showing that it greatly influences the density of APBs. On 0.5° offcut substrates, we obtained smooth, slightly tensile strained (R = 106%) GaAs epilayers that were single domain (e.g., without any APB), showing that it is not necessary to use large offcut substrates, typically 4° to 6°, for GaAs epitaxy on silicon. These make the GaAs layers more compatible with the existing silicon manufacturing technology that uses “quasi-nominal” substrates.