In this work, a surface roughness study on the die-sinking electrical discharge machining (EDM) of siliconised silicon carbide (SiSiC) has been carried out. The selection of the abovementioned conductive ceramic was made taking into account its wide range of applications in the industrial field: high temperature gas turbines, bearings, seals and lining of industrial furnaces. This study was made only for the finish stages, due to the enormous importance that a good surface quality has over such important properties as, in the case of ceramic materials: corrosion, fatigue and wear resistance. The present study has been carried out on the influence of five design factors: intensity supplied by the generator of the EDM machine (I), pulse time (ti), duty cycle (η), opencircuit voltage (U) and dielectric flushing pressure (P), which are the most relevant parameters to be controlled by the EDM process machinists, over two roughness parameters such as Ra and Rq. The study of the behaviour of the two previously mentioned parameters has been done by means of the technique of design of experiments (DOE), which allows us to carry out the previous analysis performing a relatively small number of experiments. In this case, a 25-1 fractional factorial design, whose resolution is V, has been selected due to the number of factors considered in the study.