Periodic diameter modulation of carbon nanotubes (CNTs) by quick temperature variation was successfully achieved in laser-assisted chemical vapor deposition process. Tapered and diameter-alternating CNTs were grown by periodic modulation of the temperature due to inverse relationship between the temperature and the diameter of the CNTs. The diameter-modulated single-walled carbon nanotubes (SWNTs) were integrated into field-effect transistors (FETs) structure to investigate their electronic transport properties. The tapered SWNTs showed electronic properties similar to Schottky diodes indicating clear evidence of different bandgaps at two ends of the tubes. However, the electronic transport of the diameter-modulated SWNTs showed a very small current magnitude which is attributed to the large number of defects and the electron confinement in the periodic quantum well arrays. Transmission electron microscopy and Raman spectroscopy were also studied to investigate the structural and electronic properties of the structures.