A semiconductor package, which secures the protection of circuit elements from the external environment, is disclosed. A single in-line package (SIP) is constructed by fixingly sealing a hybrid integrated circuit component within a casing with epoxy resin. A sleeve is bonded on the surface of a ceramic substrate. The sleeve is formed with silicon rubber into a pocket shape so as to cover respective circuit elements of the hybrid integrated circuit component. In the sleeve is made an opening part. Silicon gel is poured into the sleeve as a fixingly sealing material and cured to seal the respective circuit elements. Terminals downwardly extends in parallel with each other from an end part of the ceramic substrate through an opening part of the casing.