An integrated microwave transistor amplifier includes a AlGaN/GaN active transistor arrangement on a thinned Si 1-mil heat spreader. Elongated, plated-through vias extend from the source portions of the transistor arrangement through the spreader to a thick gold supporting layer. A matching circuit is defined on a four-mil GaAs substrate, also with a thick gold support layer. A stepped heat sink supports the matching circuit and the active transistor with surfaces coplanar. Bond wires interconnect the matching circuit with the gate or drain connections of the transistor.