High volume fraction Al/Sip composites are attractive for electronic packaging applications owing to their low density and coefficient of thermal expansion (CTE), together with their good thermal conductivity (TC) and flexural strength. In this study, the effects of sintering temperature, particle (Sip) size, and volume fraction (vol.-%) on the properties of Al/Sip composites produced by hot pressing were investigated. Pure Al powders were mixed with 75-85 vol.-%Sip with average particle sizes of 42 and 15 μm were hot pressed at 500°C and 620°C for 20 min. The results indicate that composites sintered in the liquid phase show higher relative density, TC, and flexural strength than those sintered in the solid phase. However, the CTEs were lower when sintered in the liquid phase than in the solid phase. As the volume fraction of Sip was increased, lower values of CTE, TC, and flexural strength were obtained. For a given volume fraction of Sip, finer Si particles result in a lower CTE and an improvement in the flexural strength of the composites.