Silicon/aluminum(Si/Al)composite is a kind of lightweight electronic packaging material that received a lot of attention in the past 20 years.In this paper,a series of Si/Al composites with lowered coefficient of thermal expansion(CTE)and high thermal conductivity were produced by powder metallurgy(PM).The Si/Al com-posites are fully dense and have fine Si particles uniquely distributed within pure Al matrix.Three 50％Si/Al com-posites were designed to have strength in the range of 185-290 MPa to meet different demands,while the other properties keep invariable.Fracture toughness of the composites is measured to be 9-10 MPa·m1/2.The com-posites were machined to 50％Si/Al housings and 27％Si/Al lids.Both the hermeticities of housings before and after laser-beam-welding sealing are determined.The measured leak rate of composites and sealed housings is in magnitude order of 1 × 10-10 and 1 × 10-9 Pa·m3?s-1,respectively,suggesting high hermeticity.The good hermeticity is attributed to the full dense materials,good weldability,and extremely low weld porosity.The present Si/Al composites are expected to be extensively used in highly hermetic electronic packages.