A multibeam semiconductor laser diode having: an n-type semiconductor substrate; an n-type clad layer, an active layer, a p-type clad layer and a contact layer; a plurality of partitioning grooves extending from one end to the other end of the substrate and formed from the contact layer to a predetermined depth of the p-type clad layer; a stripe-shaped ridge sandwiched between two separation grooves; an insulating layer covering an area from each side wall of the contact layer of each ridge to an end of the partitioning region via the separation groove; a first electrode formed on a second plane of the substrate; and a second electrode formed in each partitioning region covering an area above the ridge, separation grooves and multilayer semiconductor layers outside the separation grooves, the second electrode being constituted of a lower second electrode layer and an upper second plated layer.