A method is provided of producing inorganic semiconducting nanoparticles having a stable surface. The method comprises providing an inorganic bulk semiconductor material, such as silicon or germanium, and milling the bulk semiconductor material in the presence of a selected reducing agent. The reducing agent acts to chemically reduce oxides of one or more component elements of the semiconductor material, or prevent the formation of such oxides by being preferentially oxidised, thereby to provide semiconducting nanoparticles having a stable surface which allows electrical contact between the nanoparticles. The milling may take place in a mill in which the milling media and/or one or more components of the mill comprise the selected reducing agent. For example, the milling can be carried out in a high energy mill with a hammer action in which a pestle of the mill, a mortar of the mill, or both are composed of the selected reducing agent, or a low energy, stirred media mill, such as a ball mill, a rod mill or similar, in which the milling media, a lining of the mill, or both are composed of the reducing agent. The milling media or mill are typically composed of a metal selected from the group comprising iron, chromium, cobalt, nickel, tin, titanium, tungsten, vanadium, and aluminium, or an alloy containing one or more of said metals. In another embodiment of the method, the selected reducing agent comprises a liquid contained in the mill during milling of the bulk semiconductor material. The liquid is typically an acidic solution containing any of hydrochloric, sulphuric, nitric, acetic, formic, or carbonic acid, or a mixture thereof. The invention extends to a mill for carrying out the method.