In this paper are presented results of mutual comparison of the switching waveforms and energy losses, recorded during the turn-on and turn-off switching transients in GaN HEMTs. Switching losses were examined with the double-pulse test, using a SPICE computer simulation program. Detailed simulation models of one each cascode and enhancement-mode GaN HEMTs were used. Generated simulation results were compared with the experimental results procured on a bridgeless totem-pole power factor correction circuit, utilising the tested cascode GaN HEMT. While cascode HEMTs, in general, demonstrated higher switching losses, e-mode transistors were much more prone to the subcritically dumped oscillatory response during the hard switching. Influences of the implemented packaging and technology on the recorded response of cascode and e-mode HEMTs were analysed.