Examples of a semiconductor device includes a transistor region formed in a semiconductor substrate having a first conductivity type drift layer, and a diode region formed to be adjacent to the transistor region in the semiconductor substrate, wherein the diode region has a second conductivity type anode layer formed on the drift layer and a first conductivity type cathode layer formed on the lower side of the drift layer, and the cathode layer has an adjacent region contacting the transistor region, the adjacent region having a depth, from a lower surface of the semiconductor substrate, which becomes shallower toward the transistor region and having first conductivity type impurity concentration which decreases toward the transistor region.