This master’s project is based on the Literatures review of the light induced properties of GaAs semiconductor. It basically addresses the parameters, like energy band gap, wave length, temperature dependency, external photon energy. According to Gregor et al in semiconductors and semi metals the band gap energy of GaAs is 1.42eV, which correspond 900nm wavelength. Literatures shows that when an external temperature increases on this semiconductor decreases the band gap energy. It is also possible to increase the efficiency of the GaAs by adding the impurity to this semiconductor. PL spectra were used to investigate to characterize GaAs using external laser photon energy, energy band gap, and the type of radiation transitions. The characterization was carried out at a temperature of 300 K and 77 K with power variation in the range 40-150 mW. Then, the wavelength and band gap energy were calculated. The values of the band gaps energies were 1.4222 – 1.519 eV. Key words: GaAs semiconductors, laser photon energy, PL spectroscopy, Energy band gap, external temperature, and Energy band gap