A composite member suitable for a heat radiation member of a semiconductor element and a method of manufacturing the same are provided. This composite member is a composite of magnesium or a magnesium alloy and SiC, and it has porosity lower than 3%. This composite member can be manufactured by forming an oxide film on a surface of raw material SiC, arranging coated SiC having the oxide film formed in a cast, and infiltrating this coated SiC aggregate with a molten metal (magnesium or the magnesium alloy). The porosity of the composite member can be lowered by improving wettability between SiC and the molten metal by forming the oxide film. According to this manufacturing method, a composite member having excellent thermal characteristics such as a coefficient of thermal expansion not lower than 4 ppm/K and not higher than 10 ppm/K and thermal conductivity not lower than 180 W/m·K can be manufactured.