We measured the emission of (In,Al) GaNfilms under high intensity optical pumping both in the direction parallel and perpendicular to the film growth. In the edge emission geometry we determine the gain magnitude from the variable stripe length method. We use the spontaneous emission collected perpendicular to the layer plane to calculate the spectral dependence of the gain. Finally, we compare the emission spectra with those obtained for high quality GaAsthin films and find that the observation of a stimulated emission peak perpendicular to the nitride layer plane is predominantly due to scattering of the in‐plane stimulated emission.