Optical semiconductor device and method of manufacturing optical semiconductor device

An optical semiconductor device comprising:

• a mesa structure having a first conductivity type cladding layer, an active layer and a second conductivity type cladding layer in this order on a first conductivity type semiconductor substrate;
• a first burying layer that buries both sides of the mesa and is a different conductivity type from the first conductivity type cladding layer;
• a partially depressed upper face, of the second conductivity type cladding layer, provided from its end part, the depressed face being parallel to an upper face of the active layer;
• a second burying layer provided on the depressed face of the second conductivity type cladding layer and on the first burying layer, the second burying layer being the first conductivity type;
• and
• a shortest distance area between the active layer and the second burying layer being the depressed part of the second conductivity type cladding layer, being substantially rectangular and being located on an upside of the active layer.