QuinStar Technology proposes to develop a high-efficiency, 4-W SSPA operating at F-band frequencies (106-114 GHz). This will be achieved by employing two major innovations. Firstly, we are employing state-of-the-art wide bandgap GaN (Gallium Nitride) devices. At millimeter-wave frequencies, these GaN devices have demonstrated power densities of 5 to 8 times higher than GaAs or InP devices. Further, we are proposing to operate these devices in a quasi-switching mode, which has demonstrated, in Phase I simulations, drain efficiencies approaching 70%. The resulting MMIC, operating over the 106 to 114 GHz band, will produce an output power of one watt and an efficiency of greater than 33%. Secondly, we are proposing to utilize a new low loss, H-tee combining approach to combine 4 of these high-efficiency chips to achieve 4 watts. The net result is a unique combination of high performance devices and innovative power combining. We anticipate that this work will result in an order of magnitude increase in the state-of-the-art of SSPA output power and efficiency at F-band. We anticipate that this work will be very important for NASA's Earth Science missions and for DoD W-band radar and communications applications.