In this study, we investigated GaN channel layer quality to suppress drain-lag, which is an important parameter for switching performance. In this experiment, we confirmed that drain-lag performance has dependence on the tilt of the GaN channel layer. GaN channel layer with the tilt angle of 243 arcsec showed faster drain-lag recovery than the tilt angle of 209 arcsec. The results of the drain-lag test and isolation leakage current measurement indicated that the tilt angle and hopping distance contributed to drain-lag recovery. We proposed the mechanism of trap effect during the drain-lag test.