A method of manufacturing a lateral transistor which comprises the steps of forming N type semiconductor silicon layer on P type semiconductor substrate, depositing base region on part of the semiconductor silicon layer, forming field oxide layer bearing an opening on the base region, forming thin insulation layer on that part of the semiconductor body which is exposed by the opening, forming an annular pattern on the thin insulation layer, implanting a P type impurity in the base region, thereby providing an emitter region and collector region in the self-aligned fashion with respect to the annular pattern, retaining the annular pattern, and depositing insulation layer on the resultant structure, boring an emitter contact hole having a smaller diameter than the outer diameter of the annular pattern, and forming emitter contact hole in the self-aligned fashion with respect to the annular pattern, and forming emitter electrode in contact with the emitter region through the contact hole.

Lateral type semiconductor devices are provided which can withstand a high applied reverse voltage and can be effectively employed in semiconductor integrated circuits with an enhanced integration density. These lateral type semiconductor devices include therein an island region formed in a semiconductor supporting region and a diffusion region formed in the island region. The radius of curvature at the pn junction surface of the diffusion region is selected to be at least 1.5 times larger than the depth of the diffusion region. The diffusion region includes electrode mounting portions of large area and the remaining portions having the form of a fine line.