Microwave energy deposition is a novel method for flow control in high speed flows. Experiments have demonstrated its capability for beneficial flowfield modification in su- personic flow including, for example, drag reduction for blunt bodies. A fully three- dimensional, time-accurate gas dynamic code has been developed for simulating microwave energy deposition in air and the interaction of the microwave-generated plasma with the supersonic flow past a blunt body. The thermochemistry model includes 23 species and 238 reactions. The code is applied to the simulation of microwave energy deposition in supersonic flow past a hemisphere cylinder. The computed centerline surface pressure is compared with experiment. The interaction of the microwave-generated plasma with the flowfield structure is examined.