Half‐ring waveguides (5 &mgr;m width, 185 &mgr;m radius) fabricated by liquid‐phase expitaxial growth of Ga1−xAlxAs and GaAs layers over preferentially etched channels in GaAs substrates were made to lase by optical pumping with a N2laser (&lgr;=3371 A˚) at 77 °K. The half‐ring lasers had a threshold of about 2×104W/cm2; a bending loss per radian &agr;c<1.5 cm−1; strong TE polarization; and a well‐defined circumferential mode structure: &Dgr;&lgr;≃1.07 A˚ at &lgr;=8280 A˚ for a 580‐&mgr;m‐long cavity. Straight guides of similar profile to the circular guides were made to lase for comparison. A calculated 0.5‐A˚ mode broadening due to transient heating during the pump laser pulse accounts for the observed lasing spectra.