Impact ionization effects on hole trapping phenomena In high electron mobility transistor (HEMT) is investigated. For the purpose, measurement and a trap model simulation was done for two test devices. Measured and simulated hole trapping time constant and hole trap voltage for the two test devices are calculated and their dependence on drain bias are explored to correlate the effect of impact ionization on hole trapping phenomena. The model usability for device with different impact ionization behaviour is explored.