Abstract: The polarization effects in GaN-based HFET are analyzed on the basis of crystal structure and microelectronics theory. The characteristics, origin and magnitude of two dimension electron gas induced by polarization are reviewed, and methods to increaseits magnitude are outlined. Three typical examples of current collapse are given, and the cause of formation and suppression of collapse together with a comparison of the various techniques of suppressionare discussed. The effects of the field modulating plate on the electrical characteristics, including the breakdown voltage and RF power characteristics, are examined, from which it can be seen that GaN-based HFETs with a field modulating plate hold great promise for RF power devices.