Semiconductor device

A semiconductor device according to this disclosure comprises: a base that has a first surface and a second surface on the side opposite the first surface, and that has formed therein a penetrating hole that penetrates from the first surface to the second surface; a lead that passes through the penetrating hole and extends to the first surface side of the base; a sealing body that fills the space between the lead and lateral surfaces of the base which form the penetrating hole; a dielectric substrate having a first main surface provided upright with respect to the first surface of the base, and a second main surface that is the surface opposite the first main surface and that is provided upright with respect to the first surface of the base; a semiconductor laser provided on the first main surface-side of the dielectric substrate; a signal line that is provided on the first main surface of the dielectric substrate, and that is electrically connected to the semiconductor laser; a connecting member that electri