The authors present the largest recorded output power for a quasi-optical power-combining array and a new planar heterojunction bipolar transistor (HBT) grid amplifier design. A 16-element MESFET grid oscillator has been fabricated that generated an effective radiated power of 28 W at 9.21 GHz. The total radiated power was estimated to be 2.0 W, giving a DC to RF efficiency of 28%. A new planar grid amplifier is also presented that is suitable for monolithic fabrication. The planar amplifier grid is a hybrid design using HBT transistors monolithically fabricated in a differential pair configuration and wire bonded to a Duroid substrate. The grid amplifier had a measured gain of 11 dB at 9.9 GHz.