AGaussian approximation of the emission from a semiconductor laseris investigated by using the plane wave spectrum representation of the electric field. A Gaussian spectrum, which fits either the spectrum of the laser emission or its homogeneous component at the laser-air interface, is determined. The spread of a Gaussian function closely approximating the amplitude of the far field is obtained. The results show good agreement between the spread calculated for the Gaussian spectrum and that for the spectrum of the laser emission. The formulations and calculations are mainly carried out for a symmetric structure. The effect of the reflection at the laser-air interface and that of the asymmetry of the structure are also discussed.