Failure of patterned multiwalled carbon nanotubes during field emission (FE) was systematically studied at different fields using an indigenous FE setup. Here, the findings are reported from the experimental observation of the degradation of carbon nanotube (CNT) based field emitters over a silicon substrate. The CNTs were grown on the patterned silicon substrate using chemical vapor deposition (CVD) and plasma-enhanced CVD (PECVD) techniques. Scanning electron microscopy (SEM) was employed to observe the effect of different fields over CNTs. The observed current density of 28 mA/cm(2) at a field of 5 V/mu m from CNTs grown via CVD before giving a high-field treatment remained almost the same until the substrate started melting. Similar observations were made in CNTs grown via PECVD. SEM images clearly reveal that the high-field treatment resulted in melting of silicon substrate at a certain point; at some other points, etching of silicon substrate was also observed. The authors attribute these observations to arcing because the base vacuum was not sufficiently adequate for the applied field. Due to arcing, the localized temperature became so high that the substrate started to melt. The SEM images give an insight into understanding the degradation mechanism of CNT-based field emitters. (C) 2007 American Vacuum Society.