NOVELTY - An organic/inorganic composite comprises a silicon substrate formed with nanorods or nanoholes, and three-dimensional networks of carbon nanotubes (CNTs) grown horizontally in parallel and suspended between the adjacent nanorods or inside the nanoholes.    USE - As organic/inorganic composite useful in electronic device selected from electron emission sources, field emission displays (FEDs), light-emitting devices, light-receiving devices, solar cells, fuel cells and sensors (claimed).    ADVANTAGE - The organic/inorganic composite exhibits increased surface area and enhanced electron transfer efficiency. In the organic/inorganic composite, the metal catalysts can be uniformly formed on the nanorods or inside the nanoholes, irrespective of the height of the nanorods or the depth of the nanoholes and the shape and aspect ratio of the nanoholes or nanoholes. In addition, the carbon nanotubes grow in a three-dimensional network structure directly over the entire surface of the nanorods or the whole inner surface of the nanoholes and are directly connected to the base electrodes. With this configuration, the three-dimensional carbon nanotube networks are highly dense per unit volume, and the organic/inorganic composite is highly electrically conductive and has a large surface area. Therefore, the use of the organic/inorganic composite enables the fabrication of an electronic device with greatly improved efficiency. The carbon nanotubes are highly densely formed per unit volume in the organic/inorganic composite and are directly connected to the conductive substrate at ends, resulting in improved conductivity of the organic/inorganic composite. Therefore, the organic/inorganic composite can be directly applied to a variety of electronic devices. In contrast, despite the use of the silicon substrate in the method, the catalysts are protected from inactivation to grow three-dimensional networks of carbon nanotubes in high density even at the lowest portions of the nanorods or the nanoholes. The nanorods act as base electrodes. Since the carbon nanotubes are directly connected to the base electrodes, high conductivity of the organic/inorganic composite is achieved. As the number of the carbon nanotubes per unit space increases, the electrical conductivity and surface area of the organic/inorganic composite increase.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for preparing an organic/inorganic composite involving a) preparing an iron-molybdenum (Fe-Mo) catalyst solution; b) treating a silicon (Si) substrate formed with nanorods or nanoholes with piranha solution, UV-ozone or oxygen plasma to modify the surface of the Si substrate into Si-OH; c) dipping the surface-modified substrate in the catalyst solution to adsorb the metal catalysts on the substrate; and d) supplying a carbon source gas to the substrate adsorbed by the catalysts to produce carbon nanotubes in a three-dimensional network structure.