The constant increase in power and heat flux densities encountered in electronic devices fuels a rising demand for lightweight heat sink materials with suitable thermal properties. In this study, discontinuous pitch-based carbon fiber reinforced aluminum matrix (Al-CF) composites with aluminum–silicon alloy (Al–Si) were fabricated through hot pressing. The small amount of Al–Si contributed to enhance the sintering process in order to achieve fully dense Al–CF composites. A thermal conductivity and CTE of 258 W/(m K) and 7.0 × 10^-6/K in the in-plane direction of the carbon fibers were obtained for a (Al_{95 vol%} + Al–Si_{5 vol%})-CF_{50 vol%} composite. Carbon fiber provides the reducing of CTE while the conservation of thermal conductivity and weight of Al. The achieved CTEs satisfy the standard requirements for a heat sink material, which furthermore possess a specific thermal conductivity of 109 W cm³/(m K g). This simple process allows the low-cost fabrication of Al–CF composite, which is applicable for a lightweight heat sink material.