Four types of emission spectra from stripe-geometry GaAs-GaAlAs double hetero-tructure lasers are described and their origin studied. It has been found that the multimode configuration is caused by the nonuniformity in the active region and its adjacent area. Mode shift and competition have been measured at different current levels. We have noticed that wavelengths shift toward the shorter ones with the increase of the current. The experimental results for devices with higher thermal resistance are contrary to the above conclusions.