In magneto-plasma-dynamic (MPD) arc jet generators, plasma is accelerated by electromagnetic body forces. Silicon nitride reactive spraying was carried out using an MPD arc jet generator with crystal silicon rods and nitrogen gas. Because higher-velocity, higher-temperature and higher-density and larger-area plasmas are produced with the MPD arc jet generator than those with conventional thermal plasma torches, nitriding of silicon can be enhanced. A dense and uniform β-Si3N4 coating 30 µm thick was formed after 200 shots at a repetitive frequency of 0.03 Hz with a discharge current of 9 kA and a substrate temperature of 700 °C. The Vickers hardness reached about 1300. Furthermore, silicon carbide and aluminum nitride sprayings were conducted with the same spraying system. Surface modification is under study with lots of chemically reactive gases. All results showed that the MPD arc jet generator had high potential for spraying and surface modification.