Regular arrays of vertically aligned microstructures consisting of entangled carbon nanotubes (CNTs) of different height and contact interface were grown on Si substrates with a bimetallic catalyst by water-assisted chemical vapor deposition. The arrays of high and wide CNT blocks (150–300 μ m, 50–140 μ m square) showed the ability to reach high stable field emission (FE) currents per block up to 300 μ A due to the presence of multiple CNT emitters. However, significant outgrowth of the CNTs and limited mechanical stiffness of such blocks led to a limited FE homogeneity and alignment of the emitters. For the arrays of small rounded CNT bundles ( ∼ 5 μ m, 20 μ m diameter), well-aligned and highly efficient FE with maximum currents up to 40 μ A per CNT bundle have been achieved. Unusual I - V curves with current saturation, strong activation effects and glowing spots just before destruction have been observed and are discussed by means of band structure considerations.