In this paper silicon-on-glass VDMOSFETs are electrothermally characterized for the first time. The silicon-on-glass transistors are compared with the corresponding bulk-silicon devices by means of electrical measurements of the thermal resistance, and numerical thermal simulations. Very large values of R(TH) are measured on-wafer for each SOG VDMOSFET under test. Nevertheless, the simulations show that the electrothermal feedback is expected to be significantly reduced after the devices are mounted on a thermally conducting PCB. They indicate that the surface mounted SOG VDMOSFETs should have at least as good thermal stability as a bulk-Si VDIVIOSFET with the wafer thickness of only 100 mum.