NH_x/OH surface groups of four different commercial silicon nitride powders produced by two different methods: diimide precipitation and carbothermal reduction with different nitriding media were determined by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. The results show that for both methods the nitriding media has a profound effect on the powders surface composition. In silicon nitride powders produced using NH₃ as nitriding media in both methods, surface hydrogen content in the form of NH_x/OH groups is larger than for a powder using N₂ in the carbothermal reduction process. The intensity of NH and NH₂ groups identified and quantified by DRIFT (this work) correlate with the amounts of N₂ desorbed molecules above 1300°C and NH₃ desorbed molecules below 1300°C, measured by temperature programmed desorption mass spectroscopy (TPDMS) for the same powders, respectively. It is concluded that the NH structures form part of the surface layer.