Semiconductor device, manufacturing method thereof and power conversion device

The invention provides a semiconductor device, a manufacturing method thereof and a power conversion device. The semiconductor device includes: a semiconductor layer having a first side surface and a second side surface opposite to each other, the semiconductor layer being divided into a transistor region for constructing a transistor and a diode region for constructing a diode, the semiconductor layer including a plurality of source regions located inside a region where the transistor region is located in the first side surface thereof; the plurality of first grooves are formed in the region, where the transistor region is located, of the first side surface of the semiconductor layer, gate structures are arranged in the plurality of first grooves respectively, and the gate structures are connected with the source region; the second grooves are formed in the area, where the diode area is located, of the first side surface of the semiconductor layer, and dummy gate structures are arranged in the second grooves