In the current work, the effect of quantum confinement in the band structure of semiconductor nanotubes is investigated. The confinement of electrons in the momentum space is incorporated in sp 3 s∗ model to determine band structure of the nanotubes. The spherically symmetric r-point of nanotube energy bands is observed to split into cylindrically symmetric r′ and spherically symmetric r″ points due to confinement in transverse directions. Such splitting of r-point leads to increase the band gap ofnanotubes which further increases to a large extent with the decrease of nanotube core diameter and wall thickness. Such semiconductor nanotubes exhibit novel properties which can be exploited for developing novel quantum electronic devices. © 2018 IEEE.