Here we have demonstrated the structural effect of single wall carbon nanotubes (SWCNTs) on gas sensing and field emission properties. Vertically aligned single wall carbon nanotubes (VA-SWCNTs) and randomly oriented single wall carbon nanotubes (RO-SWCNTs) have been grown successfully on Silicon (Si) substrate at an operating temperature of 6500C by plasma enhanced chemical vapour deposition (PECVD) technique. For material characterization, Field emission scanning electron microscope (FESEM), High resolution transmission electron microscope (HRTEM) and Raman Spectroscopy have been applied. Two sets of sensors were fabricated. One set of sensors was from ROSWCNTs and other set was from VA-SWCNTs. A surprising enhancement in sensor response (200- 250%) was achieved by RO-SWCNTs sensor while for VA-SWCNTs sensor it was observed (80-100%) at constant concentration NH3 (40ppm) and at a temperature of (400C). Concentration and temperature dependent study was also conducted. Fast response/recovery time characteristics with high quality repeatability, long term stability was observed in sensitivity. The selectivity was also tested and it was found that the as fabricated sensors are more selective towards NH3 In addition of this, an excellent field emission enhancement with field enhancement factor 1.2×104 at turn on voltage 2.8 V/m and with current density 3mA/cm2 was measured by VA-SWCNTs while for RO-SWCNTs the field enhancement factor was calculated 3.8×103 at turn on voltage 4V/m with current density 1.7mA/cm2 having long term constant field emission stability. On account of this, we observe that RO-SWCNTs are better for gas sensors and VA-SWCNTs structures are better for field emission display devices. Both kind of structures have importance in respective fields. Keywords: VA-SWCNTs; RO-SWCNTs; Gas sensing; Field Emission