be repeated by inserting more alternating layers of dope al 0 3 ga 0 7 as and undoped gaas the resulting structure would have a conduction band edge diagram similar to a series of copies of fig2 the advantage of such a multiple layer structure would be an increase in the current carrying capability the problem with device 11 is the necessary inclusion of inverted structures i e the junction between layers 17 and 19 such inverted structures do not perform as expected and they degrade the overall performance of device 11 and similar devices a first preferred embodiment of the inventive device denoted generally 41 is illustrated in schematic cross section in fig3 device 41 includes a semi insulating gaas substrate layer 43 an undoped gaas layer 45 which is one micron thick an undoped al 0 3 ga 0 7 as layer 47 which is 70a thick an n type doped al 0 3 ga 0 7 as layer 49 which is 500a thick and doped in 1e18 layer 51 which is 500a thick and is composed of undoped al x ga 1 x as with x continuously varying between 0 and 0 3 from top to bottom of layer 51 layer 53 which is undoped gaas 500a thick layer 55 which is undoped al 0 3 ga 0 7 as and 70a thick layer 55 is analogous to layer 47 layer 57 which is n type al 0 3 ga 0 7 as 500a thick and doped to 1e18 layer 59 which is heavily doped n type gaas 100a thick and for electrical contact purposes region 61 which is the source metallization region 63 which is the drain metallization both regions 61 and 63 making ohmic contact and region 65 which is.