A semiconductor device according to the present invention includes a ceramic substrate, a plurality of circuit patterns arranged on a surface of the ceramic substrate, a semiconductor element arranged on an upper surface of at least one circuit pattern, and a sealing resin for sealing the ceramic substrate, the plurality of circuit patterns, and the semiconductor element, in which an undercut part is formed in opposed side surfaces of the circuit patterns adjacent to one another, the undercut part is configured such that an end of an upper surface of the circuit pattern protrudes outside the circuit pattern more than an end of a lower surface of the circuit pattern on the ceramic substrate, and the undercut part is also filled with the sealing resin.