Smaller packaging and sizing of power electronics and higher operating temperatures of switching devices call for an analysis and verification on the impact of the parasitic components in these devices. Found drift mechanisms in an eGaN-FET are studied by literature and related to measurements performed in extreme temeprature conditions far beyond the manufacturer recommended operating range. A thermal chamber was build to precisely measure the effect of temperature in these devices using a curve tracer. It is found that the increment in RDSon, IDSS, IGSS and VSD can be justified by the theory and backed up by measurements. It is also found that the particular eGaN-FET can be suited for extreme temperature operating conditions.