We present the successful fabrication of horizontally grown and dense carbon nanotube (CNT) membranes in situ. A TiN/Al2O3/TiN stack is first patterned to be employed as a support for the CNT growth. Iron is then evaporated with a 45 degrees tilt angle on the stack's vertical sidewall as a catalyst material. With the use of a material selective chemical vapor deposition (CVD) growth process, dense and thin arrays of horizontally aligned CNTs are directly grown on site, from the Al2O3/Fe surface. This process enables for the wafer scale integration of dense CNT membranes as basic building blocks in devices such as micro-electromechanical systems (MEMS) for gas sensing applications. These CNT membranes, when contacted in between interdigitated electrodes over a third buried electrode, can be expected to show enhanced sensitivity for potential gas identification sensor systems due to their large detection surface and enhanced selectivity due to potential "signature" multiple readouts of target molecules interactions with the CNT membrane. (C) 2012 Elsevier B.V. All rights reserved.