We have conducted an atomic force microscopy (AFM) study of homoepitaxial silicon layers deposited on vicinal Si(001) substrates under frequently employed molecular beam epitaxy (MBE) growth conditions. Samples with different miscut angles and miscut directions were overgrown with epilayers of thicknesses up to 7500 Angstrom and subsequently examined. A previously unknown kinetic growth instability results in distinct, highly regular surface morphologies with a considerable height of up to 40 Angstrom and periods of up to 0.45 mu m. The surface morphological features can be associated with the intrinsic properties of the Si surface and show a strong sensitivity to the growth temperature. With increasing layer thickness the morphology undergoes a simultaneous steepening and coarsening process. A qualitative model is discussed to explain our experimental results.