For potential applications of carbon nanotubes (CNTs) as connectors in microelectronic devices, the process to synthesize the large area horizontally-aligned CNTs on 100 mm (4 inch) Si wafers was developed, using electron cyclotron resonance chemical vapor deposition, with CH, and H, as the source gases and Co as the catalyst. The results show that vertical and horizontal CNTs can be obtained by manipulating the electric field applied on the substrate and flow direction of the gases. In the present deposition conditions, the horizontal CNTs show better field emission properties than vertical CNTs. This may be due to the blocking effect of catalysts at the tips and to the diminishment of the effective emission area from defects of vertical CNTs body.