The thermal stability performance of a metamorphic high electron mobility transistor (MHEMT) with a double delta-doped structure is studied and demonstrated. Due to the wide-gap and high-resistivity undoped InAlAs Schottky and buffer layer, the leakage current could be effectively reduced at higher temperature. The excellent maximum drain saturation current of 544 (524) mA/mm and maximum extrinsic transconductance of 361 (312) mS/mm are obtained at 300 (510) K for a 0.6 x 100 mu m(2) gate dimension MHEMT. In addition, an excellent thermal threshold voltage coefficient (partial derivative V-th/partial derivative T) of 0.06 mV/K is found when the temperature is increased from 330 to 510 K. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3511720] All rights reserved.