A semiconductor laser diode (LD) has been disclosed, where the emission efficiency is independent on a thickness of the p-type cladding layer. The LD provides a first semiconductor region made of group III-V compound semiconductor material, a mesa region and a burying region. The burying region, disposed on the first region, buries the mesa region. The mesa region includes an active layer, a cladding layer with a first conduction type, another cladding layer with second conduction type and a contact layer with the second conduction type. The LD of the invention in the contact layer thereof contains aluminum (Al) and indium (In) for group III element, while, arsenic (As) for group V element.