High performance In0.32Al0.68As/In0.33Ga0.67As double heterojunction metamorphic high electron mobility transistors (DH-MMHEMT) have been grown by molecular beam epitaxy on GaAs substrates. An inverse step metamorphic buffer has been used to reach a relaxation rate close to 98% and a mean cross hatch of 2 nm. The DH-MMHEMT structure with a gate length of 0.1 mu m exhibits a peak transconductance of 750 mS mm(-1), a current density of 900 mA mm(-1), a current gain cutoff frequency F-t of 150 GHz and a maximum oscillation frequency F-max of 250 GHz. These results clearly demonstrate the good electron transport properties of a double heterointerface structure due to the high relaxation, the good filtering of dislocations and the good control of the inverted InGaAs/InAlAs interface.