Heat-curable silicone compositions employing a reactive silicone, a silicone hydride crosslinker and a catalyst system which includes a rhodium-based catalyst, a stabilizing system are disclosed. A combination of rhodium and platinum-based catalysts are employed as well. The compositions are low temperature curing and are capable of providing low coefficient of thermal expansion compositions. A stabilizer system which includes in combination a peroxide and an acetylenic compound is also disclosed.