The electrical and optical properties of metamorphic InGaAs/InP composite channel high electron mobility transistor (HEMT) structures subjected to rapid thermal annealing (RTA) are systematically investigated in the temperature range of 350-650 degrees C. The metamorphic structures exhibit different degradation behaviors in different temperature ranges as compared to lattice-matched (control) structure. For the samples annealed at temperature lower than 550 degrees C, increase in annealing temperature results in a larger degradation of sheet carrier density (n(s)) and photoluminescence (PL) intensity. However, no further reduction of n, was observed in the metamorphic samples after RTA at temperature higher than 550 degrees C. An improvement of PL intensity in the temperature range of 550-650 degrees C for metamorphic samples was even observed. This behavior is absent in the lattice-matched HEMT structures. Possible mechanisms governing the change of the electrical and optical properties in metamorphice HEMT structures are discussed. Our experimental results reveal that, compared to the lattice-matched structures, the InP HEMT structures grown on GaAs using metamorphic structure could present similar thermal stability up to 650 degrees C even though a metamorphic strain-relief buffer is included. This may partially ease the concerns on the thermal stability of the metamorphic HEMT structures. (c) 2006 American Vacuum Society.