In sp3 hybridization one s and three p orbitals are involved in hybridization.
Hybridization is the process of combining two atomic orbitals with the same energy levels to produce a degenerated new type of orbitals. The atomic orbitals of similar energy are mixed together during the hybridization process, such as mixing two ‘s’ orbitals or two ‘p’ orbitals, or mixing a ‘s’ orbital with a ‘p’ orbital or a ‘s’ orbital with a ‘d’ orbital.
A tetrahedral hybridization, or sp3 hybridization occurs when one ‘s’ orbital and three ‘p’ orbitals belonging to the same shell of an atom combine to form four new equivalent orbitals. Sp3 hybrid orbitals are the new orbitals that have formed.