The radiative recombination coefficient is introduced in spontaneous emission phenomena of GaAs samples. For the spontaneous emission phenomena of streamer in high gain GaAs photoconductive semiconductor switch (PCSS), the average radiative recombination coefficient, (883)≈0.1125, is approximately determined by the simple average method and the normalization conditions. The relationship between radiative recombination coefficients of different radiation wavelengths and the average radiative recombination coefficient is derived. The radiative recombination coefficient of 890 nm radiation, η(890)=0.1182, is calculated. The maximum optical output energy calculated by substituting the value of η(890) coincides with the result of experimental observations. This demonstrates that the approximation method and the results are reasonable.