Blue-emitting nitride laser diodes have been fabricated on a-plane sapphire (1120). The active region is composed of 10 In.18Ga.82N quantum wells, which were grown by MOCVD at atmospheric and low pressure in a modified two-flow Thomas-Swan Ltd. horizontal reactor. The chemical precursors used were trimethylgallium (TMGa), trimethylindium (TMIn), trimethylaluminum (TMAI), ammonia, and disilane. The n- and p-contacts were formed by depositing Ti/Al/Ni/Au and Ni/Au/Ni/Au, respectively. Diode wafers were thinned to less than 50 μm before they were cleaved along the sapphire r-plane (1120).Lasers show TE polarization, spectral line narrowing, and far field interference patterns above the lasing threshold. The laser emission spectra peak at 410–420 nm. Under pulsed operation at room temperature, the lowest observed threshold current density was 15 kA/cm2 with threshold voltages ranging from 50–90 V. Differential efficiencies are as high as 7% with maximum output powers greater than 50 mW. Near and far field mode patterns are presented. Structures are gain-guided devices with each device occupying a mesa with a width of 125 μm. Device widths range from 3 to 20 μm, with lengths of 500 to 1200 μm.