A power combiner/divider having a waveguide, a plurality of amplifiers disposed on a supporting structure, a plurality of probes, each one having a first end electrically coupled to an output of a corresponding one of the plurality of amplifiers and a second end projecting outwardly from the supporting structure and into the waveguide. The probes are disposed in a common region of the waveguide. The region has a common electric field maximum within the waveguide. A first portion of the probes proximate the sidewalls have lengths different from a second portion of the probes disposed in a region distal from the sidewalls of the waveguide. The waveguide is supported by the support structure. The power combiner is a monolithic microwave integrated circuit structure.