Normally off lateral GaN nanowire gate-all-around MOSFETs have been fabricated on the GaN-on-insulator substrate. The dynamic measurement proved that the devices with various nanowire heights exhibit current collapse-free characteristics implying that the electrons in the isolated nanowire channel do not suffer from trapping effects. However, the dc current level measured at high drain and gate voltage is reduced to approximately one half of the value measured in dynamic mode. This is attributed to the difficulty in heat dissipation because the suspended lateral nanowire channel is thermally isolated from the substrate. However, the heat dissipation is mitigated as the nanowire size increases.