The knowledge of how the single-walled carbon nanotubes (SWCNTs) synthesis influences its structure would be of paramount importance since the structure will affect the properties of SWCNTs based device. This paper presents the synthesis of SWCNTs using thermal catalytic chemical vapor deposition technique. In the substrate preparation involving deposition of Fe catalyst, NH 3 treatment is being introduced in order to investigate the effect on the characteristic of SWCNTs. Structural characterizations were carried out using Raman spectroscopy and scanning electron microscopy (SEM). Highly crystalline SWCNTs with diameter range of 1.31 nm to 1.79 nm can be obtained from Raman spectra. The appearance of spots in SEM image seems to imply that SWCNTs are grown in bundles. It was found that SWCNTs grown with NH3 catalyst etching is highly crystalline and have narrower diameter distribution compared to the one without the treatment. This highly crystalline structure would be desirable for enhancement in the conductance of nanotubes when utilized as the sensing element in the sensor. © 2010 American Institute of Physics.