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The property of GaInN-AlGaN heterostructures and GaInN multiple quantum well (MQW) gain GaInN laser diodes with low internal loss are described. GaInN blue-violet laser diodes have been developed as a light source for optical disk recording. However, the threshold current density of these diodes has been difficult to reduce and remains high at around 3-4 kA/cm2. This is thought to be due to the large transparency current density Jt and the large optical internal loss αi. Recently, the internal loss was successfully reduced to 13.6 cm-1 by optimizing the design of the near active region and achieved stable continuous operation under 50-mW continuous wave at 70°C. Other laser characteristics such as far-field patterns and laser noise have also been improved for optical disk use.