InAlN/GaN high electron mobility transistors (HEMTs) are an attractive prospect for high reliability, high power devices for space application due the ability to lattice match the two layers, potentially removing the strain relaxation that is hypothesised to be the root of device failure, allowing for transistors with long lifetimes and high power densities. Three HEMT structures were grown by MOCVD; an InAlN/GaN each with and without an AlN interlayer and an AlGaN/GaN for comparison. Tests were undertaken to investigate the barrier composition and thickness, comparing the results to the intended values, as well as the 2DEG channel concentration, mobility and sheet resistance. The methods of testing are compared and their relative merits addressed, with uncertainties calculated where possible. Persistent photoconductivity (PPC) is considered, and then discarded based upon consecutive electrolytic C-V measurements.