The concept of using microwaves for fast semiconductor processing is known for the last three decades (Spinter et al., 1981; Scovell, 1984; Amada, 1987; Fukano et al., 1985; Zhang et al., 1994; Thompson et al., 2007). Conventional heating methods are slow because in these methods the heat is applied to the surface of the object to be heated, which needs to be transferred from the surface to the interior of the object by thermal conduction, requiring time for heating the whole object. In addition, in conventional heating methods we not only heat the object, but also the surrounding ambient, which slows down both heating and cooling rates. In contrast, microwave heating is fast because microwaves can permeate into objects heating both interior and exterior simultaneously. In addition, the ambient surrounding the object is not heated resulting in ultra-fast heating and cooling rates (Y. Tian & M.Y. Tian, 2009). It is this feature, which makes microwave heating attractive in semiconductor processing. This chapter focuses on the use of microwaves for large bandgap semiconductor material and device processing. More specifically, heating of semiconductors in a microwave cavity resonator and coupling of microwaves to a semiconductor using a microwave head are discussed. There are many applications of using microwave energy for ultra-fast thermal processing of semiconductors, such as impurity diffusion, annealing of ion-implantation generated lattice damage, ohmic contact alloying, nanowire growth etc. However, the primary focus of this chapter is on using microwave heating for annealing lattice damage in ion-implanted SiC and GaN and for growing SiC nanowires. Though microwave annealing can be used for processing any semiconductors, it is much more attractive in case of SiC, where ultra-fast heating (>1000 oC/s) to temperatures as high as 2100 oC is needed for achieving desirable electrical characteristics in ion-implantation doped material. Devices made of hexagonal polytypes of SiC and GaN are highly attractive for high-power, high-frequency and high-temperature electronic and also for optoelectronic applications.