Effect of an active layer thickness on the lateral and longitudinal modes of the gain guiding laser with a tapered stripe structure has been studied. We observed broadening in the linewidth of each longitudinal mode as well as continuous emission spectra for the tapered stripe lasers with the thicker active layer of more than 0.1 &mgr;m. From the measurement of longitudinal as well as lateral modes, it is concluded that hole burning effect is enhanced in the thicker active layer as was pointed out by Copeland. The experimental results observed for the tapered stripe lasers are inherent to gain guiding lasers with a stripe geometry structure.