Abstract: Some embodiments of the present invention provided an impedance-transforming arrangement comprising a plurality of microwave power transistors 41, and at least one intermediate impedance-transforming or matching device 30. The matching device comprises a plurality of elongate microwave transmission lines 31 provided in or on at least one dielectric substrate 32, extending across or through the dielectric substrate. The microwave transmission lines are coupled at one end to the gate pads 47 of the transistor and at the input ends to a signal input terminal for the transmission line. The transmission lines are substantially directly coupled to one another by means of resistive elements 35 providing a current flow path between the two transmission lines in order to reduce any residual tendency to instability caused by manufacturing variations or misalignment in the assembly process.