Provided is a semiconductor optical device, an arrayed semiconductor optical device, an optical module having a structure to reduce the parasitic capacitance as well as a high design degree of freedom and having a multilayer structure in which a semi-insulating substrate, a first semiconductor layer having one conductive type, an active layer having light emission function, a second semiconductor layer having the other conductive type, an insulating layer, and a conductive layer are stacked in order from the bottom. The multilayer structure includes a light emitting structure, a first electrode structure, and a second electrode structure. In the semi-insulating substrate and the first semiconductor layer, a first grove which separates the second electrode structure from a remaining portion and approaches the second electrode structure with a non-linear shape rather than a linear shape in its entirety is formed.