Patent ID: 7514727

Claim:
An active element comprising: a compound semiconductor substrate; a stack of first, second and third semiconductor layers disposed on the substrate; and a plurality of unit elements connected in parallel, each of the unit elements comprising a first transistor and a second transistor, the first transistor comprising a collector formed of the first semiconductor layer, a base formed of the second semiconductor layer and an emitter formed of the third semiconductor layer, the second and third semiconductor layers forming a heterojunction, the second transistor formed of the semiconductor layers and comprising a gate, a source and a drain, the first and second transistors being isolated by a isolation region, the base of the first transistor being connected with the source of the second transistor, and the drain of the second transistor being connected with a power supply potential, and the isolation region comprising an impurity region formed at least in the first and second semiconductor layers between the first and second transistors, and a wiring being disposed on the isolation region and connecting the base of the first transistor and the source of the second transistor, wherein electrodes of the bases, emitters and collectors are arranged to form a comb-like structure, and a longitudinal direction of teeth of the comb-like structure is different from a longitudinal direction of electrodes of the gates so that the wiring crosses neither an electrode of a collector nor an electrode of an emitter, and the electrodes of the emitters are connected by an emitter wiring running in the longitudinal direction of the electrodes of the gates.