Radio frequency (RF) packages containing substrates having coefficient of thermal expansion (CTE) matched mount pads are disclosed, as are methods for fabricating RF packages and substrates. In embodiments, the RF package contains a high thermal performance substrate including a metallic base structure, which has a frontside facing a first RF power die and a first die attach region on the frontside of the base structure. A first CTE matched mount pad is bonded to the metallic base structure and covers the first die attach region. The first CTE mount pad has a CTE greater than the CTE of RF power die and less than the CTE of the metallic base structure. An electrically-conductive bonding material attaches the RF power die to the first CTE matched mount pad, while RF circuitry integrated into first RF power die is electrically coupled to the metallic base structure through the mount pad.