Here, we present an experimental investigation of the optical spectra of single walled carbon nanotubes (SWCNT) at temperatures up to 1273 K. This investigation gives insights into the electronic structure of metallic and semiconducting SWCNT at different temperatures by measuring the shift of the S₁₁-, S₂₂- and M₁₁-band with optical absorption spectroscopy. We observed a decrease of the transition energies in both metallic and semiconducting SWCNT with increasing temperature determined by the shift of the S₁₁-, S₂₂- and M₁₁-absorption bands. The shifts follow the Varshni-equation. Furthermore, calculation of the average exciton binding energy (80-90 meV) in metallic SWCNT from the shift of the M₁₁-band was performed. We demonstrate in this paper, that the optical absorption spectroscopy is an effective tool for characterisation of the electrical properties and structure of SWCNT.