Device structures with a reduced junction area in an SOI process, methods of making the device structures, and design structures for a lateral diode. The device structure includes one or more dielectric regions, such as STI regions, positioned in the device region and intersecting the p-n junction between an anode and cathode. The dielectric regions, which may be formed using shallow trench isolation techniques, function to reduce the width of a p-n junction with respect to the width area of the cathode at a location spaced laterally from the p-n junction and the anode. The width difference and presence of the dielectric regions creates an asymmetrical diode structure. The volume of the device region occupied by the dielectric regions is minimized to preserve the volume of the cathode and anode.