A new structure for Npn GaAs heterojunction microwave bipolar transistor is proposed in this paper. The main feature of the structure is the adoption of a two layer n Ga

0.4

Al

0.6

As/Ga

0.7

Al

0.3

As double emitter instead of the normally used one layer n Ga

0.7

Al

0.3

As wide gap emitter. The layer of the low Al composition

acting as the wide gap emitter

is adjacent to the base resulting in a close matched heterojunction of the emitter and a low turn on voltage on the I-V characteristic of the transistor. The layer of the high Al composition and n

+

GaAs cap layer form a system which can be easily controlled for selective etching by hot HCl. Therefore

the self alignment structure can be obtained. This structure not only reduces the dimensions of the transistor

but also simplifies the processing of the transistor remarkably while ensuring very good characteristics (f

T

=4.6GHz

f

mag

=3.7GHz).