A curable silicone composition which can cure using hydrosilylation, comprising an aluminum oxide powder and/or silica powder, the powders each consisting of substantially spherical particles with an average particle diameter of 50 .mu.m or below and an elongation of from 1.0 to 1.4 and being such that the respective amounts of alkali metal ions and halogen ions are extracted with 50 ml of water from 5 g of the powder at 121.degree. C. for 20 hours are not more than 10 ppm, wherein the amount of the component (D) is from 25 to 90% by weight based on the composition, and the ratio of the amount of hydrosilyl groups contained in the components (A) and (B) to the amount of alkenyl groups contained in the components (A) and (B) is in the range from 0.5/1 to 1.5/1. When the composition is used as a protective material or encapsulating material for devices such as ICs, generated heat can be dissipated efficiently and the devices are not be broken by abrasion. There are no fears of causing corrosion of the devices.