A lead frame includes a first outer lead portion and a second outer lead portion which is arranged to oppose to the first outer lead portion with an element-mounting region between them. An inner lead portion has first inner leads connected to the first outer leads and second inner leads connected to the second outer leads. At least either the first or second inner leads are routed in the element-mounting region. An insulation resin is filled in the gaps between the inner leads located on the element-mounting region. A semiconductor device is configured with semiconductor elements mounted on both the top and bottom surfaces of the lead frame.