Current gas sensors are mainly categorized into two modes of operation; chemical type operating by gas adsorption and physical type using ionization method. Chemical type conductivity-based gas detectors are large in size, they operate at high temperatures, and their response time is slow. Moreover most of them are only capable of detecting single type gases due to their low selectivity. Physical type ionization-based sensors have better selectivity and response time, but they are still huge and bulky. Both chemical and physical type gas detectors are using semiconductor materials as their sensing elements. With the discovery of nanomaterials, different types of sensing elements have been investigated to produce gas sensors which are smaller in size, one of which is carbon nanotubes (CNTs). Development of high performance sensor is now focused towards CNT-based sensors because of their inherent properties such as small size, large surface area and high electrical conductivity. CNTs based sensors are smaller in size; they have lower power consumption, higher sensitivity and better selectivity compared to existing semiconducting gas sensors. CNT-based gas sensors operate in room temperature which will result in safer environment. The work investigates the structural and electrical characterization of carbon nanotubes array for suitability as an effective sensing element in the ionization-based gas sensor. © 2010 IEEE.