We demonstrate the first blue AlInGaN-based laser diodes (LDs) grown on semipolar (33) free-standing GaN substrates. Etched facet ridge waveguide LDs were fabricated and tested under pulsed operation. Lasing was achieved at 477.5 nm with a threshold current density of 12.2 kA/cm2. The peak electroluminescence wavelength was shown to blue-shift from approximately 494 nm to 477 nm upon reaching threshold. Initial experimental data also show the (33) plane to have higher indium incorporation efficiency than the (33) plane, suggesting that (33) GaN substrates may be more suitable for growth and fabrication of long-wavelength AlInGaN-based LDs than (33) GaN substrates. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)