Aligned carbon nanotube (CNT) array has been successfully synthesized from acetylene and hydrogen mixture by radio frequency (rf) plasma-enhanced chemical vapor deposition (PE-CVD) on patterned iron or cobalt coated silicon substrates. The length of the nanotubes and thus the height of the CNT arrays could be controlled by varying the growth time; the width of C the lines was controlled by the size of the openings in the shallow mask. Adjusting the thickness of the catalyst layer changes the aligned CNT density within the array. Using, the substrates with a 10-30 nm catalyst layer, the synthesized CNTs were densely packed and perpendicularly aligned. However, a thicker (more than 60 nm) or a thinner (less than 5 nm) catalyst layer resulted in a significantly reduced CNT density within the array.