A semiconductor device of an embodiment includes: a wiring board having a first surface and a second surface on a side opposite to the first surface; a first semiconductor element on the first surface of the wiring board; a second semiconductor element on the first surface of the wiring board; and a first sealing material that seals at least the second semiconductor element. A slit is formed in the first sealing material between the first semiconductor element and the second semiconductor element. When a thickness of the first sealing material on the first semiconductor element is t1 and a thickness of the first sealing material on the second semiconductor element is t2, the t1 and the t2 satisfy a relationship of 0≤t1